Hell, Linux didn't exist at all till '91.

I think Xenix was more just a casualty of the Unix Wars.  The victors there were SunOS/Solaris, AIX, and HP-UX.  There were a bunch more walking wounded that never really achieved much market share.

By the time SCO filed suit in 2003, not only were the Unix Wars fairly long over (SCO had lost), but commercial Unixes had largely been supplanted by Linux (and BSD enthusiasts had three free options, and OS X was a thing if you wanted a commercial BSD, but Apple never managed to make much in the way of inroads into the server market).  Linux's ascendency happened around the turn of the millennium, as I recall, although I was using AIX at my job as late as 2010-2011, and I presume the Big Several still exist in some form or other.