Addressing Steve Crutchfield's sequence of dates and events, a sidelight or two.
I bought II+ in 1985 (with my first computer, a 286 PC, on retirement from Britannica, where I was executive editor (inter al.). I had been introduced to its essence at EB, which had bought an adaptation of ATEX based on lengthy examination of the system used by the Jehovah's Witnesses publishing house.
A Xywrite Users Group (which also used its unlovely initials) had sprung up in Chicago, and I attended its monthly (or maybe sporadic) meetings religiously for a year or two (barely moderated self-help, or rarther mutual aid, sessions).
I bought every upgrade except XyWin, as I found (still do) Swindows a hostile environment. I watched the pre-promotion of Signature with interest and its silent subsidence with disappointment.