diff --git a/src/OpenFOAM/containers/CompactLists/CompactListList/CompactListList.C b/src/OpenFOAM/containers/CompactLists/CompactListList/CompactListList.C
index 4043af45e5..1dcd12b86c 100644
--- a/src/OpenFOAM/containers/CompactLists/CompactListList/CompactListList.C
+++ b/src/OpenFOAM/containers/CompactLists/CompactListList/CompactListList.C
@@ -35,16 +35,25 @@ template<class T>
 void Foam::CompactListList<T>::reportOverflowAndExit
 (
     const label idx,
-    const labelUList& localLens
+    const label prevOffset,
+    const label count
 )
 {
+    if (idx < 0)
+    {
+        // No overflow tagged
+        return;
+    }
+
     FatalErrorInFunction
         << "Overflow : sum of sizes exceeds labelMax ("
         << labelMax << ") after index " << idx;
 
-    if (!localLens.empty())
+    if (prevOffset >= 0 && count >= 0)
     {
-        FatalError << " of " << flatOutput(localLens);
+        FatalError
+            << " while trying to add (" << count
+            << ") to offset (" << prevOffset << ")";
     }
 
     FatalError
@@ -76,12 +85,14 @@ Foam::CompactListList<T> Foam::CompactListList<T>::pack_impl
 
         for (label i = 0; i < len; ++i)
         {
+            const label count = lists[i].size();
+
             newOffsets[i] = total;
-            total += lists[i].size();
+            total += count;
 
             if (checkOverflow && total < newOffsets[i])
             {
-                reportOverflowAndExit(i);
+                reportOverflowAndExit(i, newOffsets[i], count);
             }
         }
         newOffsets[len] = total;
@@ -162,12 +173,14 @@ Foam::label Foam::CompactListList<T>::resize_offsets
 
         for (label i = 0; i < len; ++i)
         {
+            const label count = listSizes[i];
+
             offsets_[i] = total;
-            total += listSizes[i];
+            total += count;
 
             if (checkOverflow && total < offsets_[i])
             {
-                reportOverflowAndExit(i, listSizes);
+                reportOverflowAndExit(i, offsets_[i], count);
             }
         }
 
@@ -229,8 +242,8 @@ Foam::label Foam::CompactListList<T>::maxNonLocalSize(const label rowi) const
     {
         if (i != rowi)
         {
-            const label localLen = (offsets_[i+1] - offsets_[i]);
-            maxLen = max(maxLen, localLen);
+            const label count = (offsets_[i+1] - offsets_[i]);
+            maxLen = max(maxLen, count);
         }
     }
 
diff --git a/src/OpenFOAM/containers/CompactLists/CompactListList/CompactListList.H b/src/OpenFOAM/containers/CompactLists/CompactListList/CompactListList.H
index 62b53ddb49..a912bb5767 100644
--- a/src/OpenFOAM/containers/CompactLists/CompactListList/CompactListList.H
+++ b/src/OpenFOAM/containers/CompactLists/CompactListList/CompactListList.H
@@ -82,11 +82,12 @@ class CompactListList
 
     // Private Member Functions
 
-        //- Report overflow at specified index
+        //- Report overflow at specified (non-negative) index
         static void reportOverflowAndExit
         (
             const label idx,
-            const labelUList& listSizes = labelUList::null()
+            const label prevOffset = -1,  // The last valid offset value
+            const label count = 0         // The count to add to prevOffset
         );
 
         //- Construct by packing together the list of lists
diff --git a/src/OpenFOAM/parallel/globalIndex/globalIndex.C b/src/OpenFOAM/parallel/globalIndex/globalIndex.C
index ce900d9630..bfbaa6cc80 100644
--- a/src/OpenFOAM/parallel/globalIndex/globalIndex.C
+++ b/src/OpenFOAM/parallel/globalIndex/globalIndex.C
@@ -34,16 +34,25 @@ License
 void Foam::globalIndex::reportOverflowAndExit
 (
     const label idx,
-    const labelUList& localLens
+    const label prevOffset,
+    const label count
 )
 {
+    if (idx < 0)
+    {
+        // No overflow tagged
+        return;
+    }
+
     FatalErrorInFunction
         << "Overflow : sum of sizes exceeds labelMax ("
         << labelMax << ") after index " << idx;
 
-    if (!localLens.empty())
+    if (prevOffset >= 0 && count >= 0)
     {
-        FatalError << " of " << flatOutput(localLens);
+        FatalError
+            << " while trying to add (" << count
+            << ") to offset (" << prevOffset << ")";
     }
 
     FatalError
@@ -70,27 +79,29 @@ Foam::globalIndex::calcRange
     }
 
     const label myProci = UPstream::myProcNo(comm);
-    const labelList localLens = UPstream::allGatherValues(localSize, comm);
+    const labelList counts = UPstream::allGatherValues(localSize, comm);
 
     if (checkOverflow)
     {
-        const label len = localLens.size();
+        const label len = counts.size();
 
         label start = 0;
 
         for (label i = 0; i < len; ++i)
         {
+            const label count = counts[i];
+
             if (i == myProci)
             {
                 myRange.start() = start;
             }
 
             const label prev = start;
-            start += localLens[i];
+            start += count;
 
             if (start < prev)
             {
-                reportOverflowAndExit(i, localLens);
+                reportOverflowAndExit(i, prev, count);
             }
         }
     }
@@ -98,8 +109,8 @@ Foam::globalIndex::calcRange
     {
         // std::accumulate
         // (
-        //     localLens.cbegin(),
-        //     localLens.cbegin(myProci),
+        //     counts.cbegin(),
+        //     counts.cbegin(myProci),
         //     label(0)
         // );
 
@@ -107,7 +118,7 @@ Foam::globalIndex::calcRange
 
         for (label i = 0; i < myProci; ++i)
         {
-            start += localLens[i];
+            start += counts[i];
         }
         myRange.start() = start;
     }
@@ -133,27 +144,28 @@ Foam::globalIndex::calcOffset
     }
 
     const label myProci = UPstream::myProcNo(comm);
-    const labelList localLens = UPstream::allGatherValues(localSize, comm);
+    const labelList counts = UPstream::allGatherValues(localSize, comm);
 
     if (checkOverflow)
     {
-        const label len = localLens.size();
+        const label len = counts.size();
 
         label start = 0;
 
         for (label i = 0; i < len; ++i)
         {
+            const label count = counts[i];
             if (i == myProci)
             {
                 myOffset = start;
             }
 
             const label prev = start;
-            start += localLens[i];
+            start += count;
 
             if (start < prev)
             {
-                reportOverflowAndExit(i, localLens);
+                reportOverflowAndExit(i, prev, count);
             }
         }
     }
@@ -161,8 +173,8 @@ Foam::globalIndex::calcOffset
     {
         // std::accumulate
         // (
-        //     localLens.cbegin(),
-        //     localLens.cbegin(myProci),
+        //     counts.cbegin(),
+        //     counts.cbegin(myProci),
         //     label(0)
         // );
 
@@ -170,7 +182,7 @@ Foam::globalIndex::calcOffset
 
         for (label i = 0; i < myProci; ++i)
         {
-            start += localLens[i];
+            start += counts[i];
         }
         myOffset = start;
     }
@@ -182,13 +194,13 @@ Foam::globalIndex::calcOffset
 Foam::labelList
 Foam::globalIndex::calcOffsets
 (
-    const labelUList& localLens,
+    const labelUList& counts,
     const bool checkOverflow
 )
 {
     labelList values;
 
-    const label len = localLens.size();
+    const label len = counts.size();
 
     if (len)
     {
@@ -197,12 +209,13 @@ Foam::globalIndex::calcOffsets
         label start = 0;
         for (label i = 0; i < len; ++i)
         {
+            const label count = counts[i];
             values[i] = start;
-            start += localLens[i];
+            start += count;
 
             if (checkOverflow && start < values[i])
             {
-                reportOverflowAndExit(i, localLens);
+                reportOverflowAndExit(i, values[i], count);
             }
         }
         values[len] = start;
@@ -215,13 +228,13 @@ Foam::globalIndex::calcOffsets
 Foam::List<Foam::labelRange>
 Foam::globalIndex::calcRanges
 (
-    const labelUList& localLens,
+    const labelUList& counts,
     const bool checkOverflow
 )
 {
     List<labelRange> values;
 
-    const label len = localLens.size();
+    const label len = counts.size();
 
     if (len)
     {
@@ -230,12 +243,18 @@ Foam::globalIndex::calcRanges
         label start = 0;
         for (label i = 0; i < len; ++i)
         {
-            values[i].reset(start, localLens[i]);
-            start += localLens[i];
+            const label count = counts[i];
+            values[i].reset(start, count);
+            start += count;
 
-            if (checkOverflow && start < values[i].start())
+            if
+            (
+                checkOverflow
+             && (start < values[i].start())
+             && (i < len-1)  // Do not check the one beyond the end range
+            )
             {
-                reportOverflowAndExit(i, localLens);
+                reportOverflowAndExit(i, values[i].start(), count);
             }
         }
     }
@@ -328,11 +347,11 @@ void Foam::globalIndex::reset
 
     if (len)
     {
-        labelList localLens;
+        labelList counts;
 
         if (parallel && UPstream::parRun())  // or UPstream::is_parallel(comm)
         {
-            localLens = UPstream::allGatherValues(localSize, comm);
+            counts = UPstream::allGatherValues(localSize, comm);
         }
         else
         {
@@ -340,11 +359,11 @@ void Foam::globalIndex::reset
             // TBD: check for (proci >= 0) ?
             const auto proci = UPstream::myProcNo(comm);
 
-            localLens.resize(len, Zero);
-            localLens[proci] = localSize;
+            counts.resize(len, Zero);
+            counts[proci] = localSize;
         }
 
-        reset(localLens, true);  // checkOverflow = true
+        reset(counts, true);  // checkOverflow = true
     }
     else
     {
@@ -356,11 +375,11 @@ void Foam::globalIndex::reset
 
 void Foam::globalIndex::reset
 (
-    const labelUList& localLens,
+    const labelUList& counts,
     const bool checkOverflow
 )
 {
-    const label len = localLens.size();
+    const label len = counts.size();
 
     if (len)
     {
@@ -369,12 +388,13 @@ void Foam::globalIndex::reset
         label start = 0;
         for (label i = 0; i < len; ++i)
         {
+            const label count = counts[i];
             offsets_[i] = start;
-            start += localLens[i];
+            start += count;
 
             if (checkOverflow && start < offsets_[i])
             {
-                reportOverflowAndExit(i, localLens);
+                reportOverflowAndExit(i, offsets_[i], count);
             }
         }
         offsets_[len] = start;
@@ -468,8 +488,8 @@ Foam::label Foam::globalIndex::maxNonLocalSize(const label proci) const
     {
         if (i != proci)
         {
-            const label localLen = (offsets_[i+1] - offsets_[i]);
-            maxLen = max(maxLen, localLen);
+            const label count = (offsets_[i+1] - offsets_[i]);
+            maxLen = max(maxLen, count);
         }
     }
 
@@ -506,17 +526,17 @@ Foam::labelRange Foam::globalIndex::back() const
 }
 
 
-// * * * * * * * * * * * * * * * Friend Operators  * * * * * * * * * * * * * //
+// * * * * * * * * * * * * * * * IOstream Operators  * * * * * * * * * * * * //
 
 Foam::Istream& Foam::operator>>(Istream& is, globalIndex& gi)
 {
-    return is >> gi.offsets_;
+    return is >> gi.offsets();
 }
 
 
 Foam::Ostream& Foam::operator<<(Ostream& os, const globalIndex& gi)
 {
-    return os << gi.offsets_;
+    return os << gi.offsets();
 }
 
 
diff --git a/src/OpenFOAM/parallel/globalIndex/globalIndex.H b/src/OpenFOAM/parallel/globalIndex/globalIndex.H
index 6e37dfddf3..19f6d04bf9 100644
--- a/src/OpenFOAM/parallel/globalIndex/globalIndex.H
+++ b/src/OpenFOAM/parallel/globalIndex/globalIndex.H
@@ -83,11 +83,12 @@ class globalIndex
             DynamicList<label>& validBins
         );
 
-        //- Report overflow at specified index
+        //- Report overflow at specified (non-negative) index
         static void reportOverflowAndExit
         (
             const label idx,
-            const labelUList& localLens = labelUList::null()
+            const label prevOffset = -1,  // The last valid offset value
+            const label count = 0         // The count to add to prevOffset
         );
 
 public:
@@ -122,7 +123,7 @@ public:
         //- No communication required
         inline explicit globalIndex(labelList&& listOffsets);
 
-        //- Copy construct from a list of sizes.
+        //- Construct from a list of sizes and calculate the offsets.
         //- No communication required
         inline globalIndex
         (
@@ -265,12 +266,12 @@ public:
             const bool parallel = UPstream::parRun()  //!< use parallel comms
         );
 
-        //- Reset from list of local sizes,
+        //- Reset offsets from a list of local sizes,
         //- with optional check for label overflow.
         //- No communication required
         void reset
         (
-            const labelUList& localLens,
+            const labelUList& counts,
             const bool checkOverflow = false
         );
 
@@ -307,6 +308,9 @@ public:
             const label comm = UPstream::worldComm  //!< communicator
         );
 
+        //- Reset the globalIndex. Same as copy assignment.
+        inline void reset(const globalIndex& gi);
+
         //- Alter local size for given processor
         void setLocalSize(const label proci, const label len);
 
@@ -504,7 +508,7 @@ public:
         //- with optional check for label overflow
         static labelList calcOffsets
         (
-            const labelUList& localLens,
+            const labelUList& counts,
             const bool checkOverflow = false
         );
 
@@ -521,7 +525,7 @@ public:
         //- with optional check for label overflow
         static List<labelRange> calcRanges
         (
-            const labelUList& localLens,
+            const labelUList& counts,
             const bool checkOverflow = false
         );
 
@@ -955,6 +959,27 @@ public:
         ) const;
 
 
+    // Member Operators
+
+        //- Compare for equality - uses the offsets
+        bool operator==(const globalIndex& rhs) const
+        {
+            return (this->offsets() == rhs.offsets());
+        }
+
+        //- Compare for inequality - uses the offsets
+        bool operator!=(const globalIndex& rhs) const
+        {
+            return !(*this == rhs);
+        }
+
+        //- Compare for less-than - uses the offsets
+        bool operator<(const globalIndex& rhs) const
+        {
+            return (this->offsets() < rhs.offsets());
+        }
+
+
     // IOstream Operators
 
         friend Istream& operator>>(Istream& is, globalIndex& gi);
diff --git a/src/OpenFOAM/parallel/globalIndex/globalIndexI.H b/src/OpenFOAM/parallel/globalIndex/globalIndexI.H
index 2a4da4716d..a4cd6f4e12 100644
--- a/src/OpenFOAM/parallel/globalIndex/globalIndexI.H
+++ b/src/OpenFOAM/parallel/globalIndex/globalIndexI.H
@@ -467,6 +467,16 @@ inline void Foam::globalIndex::reset
 }
 
 
+inline void Foam::globalIndex::reset(const globalIndex& rhs)
+{
+    if (this == &rhs)
+    {
+        return;  // Self-assignment is a no-op
+    }
+    this->offsets_ = rhs.offsets_;
+}
+
+
 // * * * * * * * * * * * * * * * * Iterators * * * * * * * * * * * * * * * * //
 
 inline Foam::globalIndex::const_iterator::
diff --git a/src/OpenFOAM/parallel/globalIndex/globalIndexTemplates.C b/src/OpenFOAM/parallel/globalIndex/globalIndexTemplates.C
index 19f4db5be8..3643b21850 100644
--- a/src/OpenFOAM/parallel/globalIndex/globalIndexTemplates.C
+++ b/src/OpenFOAM/parallel/globalIndex/globalIndexTemplates.C
@@ -49,12 +49,14 @@ Foam::globalIndex::calcListOffsets
         label start = 0;
         for (label i = 0; i < len; ++i)
         {
+            const label count = lists[i].size();
+
             values[i] = start;
-            start += lists[i].size();
+            start += count;
 
             if (checkOverflow && start < values[i])
             {
-                reportOverflowAndExit(i);
+                reportOverflowAndExit(i, values[i], count);
             }
         }
         values[len] = start;
@@ -1005,12 +1007,12 @@ OutputContainer Foam::globalIndex::scatter
         // The globalIndex might be correct on master only,
         // so scatter local sizes to ensure consistency
 
-        const label localLen
+        const label count
         (
             UPstream::listScatterValues<label>(this->localSizes(), comm)
         );
 
-        OutputContainer localData(localLen);
+        OutputContainer localData(count);
         this->scatter(allData, localData, tag, commsType, comm);
 
         return localData;