I did come across https://books.google.com/books?id=Gf4YAQAAIAAJ&pg=PA89&dq=%2... from 1978 ("Software Designers Workbench", Paul A. Scheffer, Martin Marietta Aerospace
> One of the more innovative of recent software engineering activities is the concept of a Programmer's Workbench (PWB)
(PWB is the term for the product which included SCCS.)
> A simple generalization of the PWB concept results in the idea of a total software engineering facility, i.e., a Designer's Workbench (DWV) ...
> Using a PDP 11/70 architecture base, and system software which includes RSX-11M and the UNIX operating systems, standard PWB tools, and INGRES data base capabilities ...
Since it looks like UNIX supported the RSX-11M in 1978, why couldn't Ericsson be using Unix on an RSX-11M at the same time in Norway?
The original version was for OS/MVT and implemented in SNOBOL4 using the SPITBOL compiler. https://apps.dtic.mil/sti/pdfs/ADA084326.pdf says that SNOBOL4 was available for the RSX-11D by 1979.
I have no clue what Ericcson was using. My inference from the literature is that apparently when software developers have access to a version control system, they used it, even back in the 1970s.
FWIW, I regard versioned file systems as a form of version control.