"(though my memory _is_ muddled, I am sure)", yes muddled. OS/2 did'nt (itself) care about memory under 640Kb but it did really require 8Mb (16Mb if you were doing serious stuff like development). The DOS sessions in OS/2 generall had a lot of under 640Kb memory available (it made good use of virtual memory).
Went from Dos 4.x to OS/2 and then Solaris/Linux. Did'nt do much with windows at all. But OS/2 years ahead of the competition, maybe just a bit too far ahead.