This web page has some details about XENIX prior to 1985:
http://seefigure1.com/2014/04/15/xenixtime.html
In particular this chart is intriguing:
http://seefigure1.com/images/xenix/xenix-timeline.jpg
I’d love to have XENIX from the 1980-1985 era in the TUHS archive, as it documents the
tail end of the Unix on 16 bits era. It would have been great if MS had released that as
part of the Unix-at-50 events.
Paul