This is fascinating to me! How did you manage to merge code in the 80s? What tools were available? Did you have three-way merge tools or did you do it more manually?
Or rather did you talk frequently and ensure that you weren't stepping in each other's files? How did you make changes to shared APIs?
Some "old-timers" at my software company occasionally tell stories about how "checking the source code" meant physically grabbing a the one binder filled with pages of fortran and inserting your changes. Physically holding the binder gave you exclusive checkin access :)
Macintosh Programmers Workshop had some tools but we mostly did it by hand so we tended to work on different parts of the program. If that was a problem our manager who owned the company would do a road trip to collect the new code that another person needed (we all lived in the Bay Area.) He had a big financial incentive to do so. Or we would get together, but that was not optimal.
There were always tools to diff two codebases and make a intermediate file that had all the changes. We did it back in the BBS days. You could always take the diff file and type the changes in manually. That's how "mods" worked. It would be something like this
SomeFile.pas
14: - If Variable = 1
14: + If Variable = 2
Or rather did you talk frequently and ensure that you weren't stepping in each other's files? How did you make changes to shared APIs?