I don't think either SCCS or RCS tracked merges, so everything looks like a new revision.

Correct. I had used both at work up until around 2005. The idiot large companies I worked at did not believe in Source Code Control. That is the one thing I liked about RCS/SCCS, once I checked out an item, no one could check in their changes unless they contacted me. Forcing a coordinated manual merge between us.

I tried to get our org on to something for a while, but got massive push back until 5 or 6 years ago when they setup corporate wide paid githup repo.

Before that, I found a small group of developers around 2005 that used CVS and they allowed me to leverage that for my group. But of course I was the only one who used it.

Back then I guess people loved loosing source code, which happened a lot until git.

also rebases instead of merges wouldn't count as merges