vi history in BSD goes back to 1980

Sources are at http://svnweb.freebsd.org/csrg/usr.bin/ex/

A bit earlier — 1977 at least¹. I guess there was some (actual or alleged) descent from ed (the standard text editor) in the AT&T kerfuffle preventing it from being generally released under a BSD license.

Keith Bostic reimplemented it from scratch as nvi (new vi) for 4BSD.

Vim's code is not descended from either of those.

¹ http://minnie.tuhs.org/cgi-bin/utree.pl?file=1BSD/ex-1.1/REA...

It’s pretty amazing to browse code repos that go back over 25 years. Does anyone know which version control system they (BSD) used back then? SCCS?

Yep, that repo was apparently converted from SCCS: http://unix.derkeiler.com/Mailing-Lists/FreeBSD/current/2012...

More likely a file server somewhere, email and patches.

After all Linux didn't use a SCM until quite late.

That's because Linus had the fairly unique position that CVS et al. are actually worse than not using a SCM at all.

The BSDs have been using CVS for a long time so it's plausible they used something like RCS or SCCS before CVS was available.

FreeBSD repo goes back to 1993: https://svnweb.freebsd.org/base?view=revision&revision=2