My first job out of college was on a university administrative system where all the source files were managed by RCS. I came on in '97, but the system had been operation in at least that state to 1995. Obnoxiously, the vendor layered some secret sauce on top of it in Makefiles for the actual checkins and outs, so you did something like `make co F=foo.c` which totally messed up filename completion. I had it aliased in tcsh within minutes to preserve my own sanity.

When my consultant contract finally came to an end in 2003 they were still using it.