The issue was the rcs files were simply corrupt - no matter what tool you used the older deltas were just bad. Just people didn't notice/care as they were "old" revisions.

And I couldn't find any tool that supported the mks "project" files that linked multiple rcs revisions into a single "commit", so something a little custom was needed anyway. At least for the ancient mks version used.

Quite a bit of effort was put into it during the "official" migration, but they eventually gave up too as even the oldest backup archives they could find had the same issues.