@evan I wouldn't have if you hadn't said what the four choices were. X.500 was slightly more accessible in my memory.
I was at Convergent Technologies when they produced the Server PC based on the then hottest CPU in town, the 386 (Intel used benchmarks run on it in ads). And Convergent produced what I think was just a port of VINES running on their Unix on the Server PC.
I mostly worked on the Server PC BIOS, modified from Phoenix code. And debugging issues with DOS programs running on it, since saying the Server PC was IBM compatible was a marketing thing that probably didn't really matter in the end. I would have been in my 20s, in my second post college job.