You're right re the dates, may be the Q-80 was the stop gap and the Q-90 was just done to use up the remaining Q-80 bodies.
By the early 90ies the Q-90 looked and sounded positively dated - no amount of face lift and new pups could change that.
Whether Marx learned anything from Lawrence I don't know - that Lawrence pushed for him in the Gibson organisation is something I learned from Phil Jones who did not seem to like either of them very much.
Re modern TBirds: I always thought that while 1987 is always given as the (re)introduction year, nothing hit the market until 1988. In 1986, TBirds were still made for Japan with the anemic Bicentennial pups and I have a Custom Shop TBird from as late as early December 1987 that features
- the old huge headstock,
- large tuners,
- output jack on the face of the body,
- a flimsily thin neck/headstock zone that even for TB standards is asking for trouble, plus
- really meek sounding - what look like - TB Plus pups, they obviously did something to those even in the 87 versions that graced the IV or V, perhaps the Custom Shop wanted to emulate the sound of the Bicentennial pups with them.
My info has been that the first reissued TBirds were all made by the Custom Shop and that production was only eased over to the regular manufacturing line after the Custom Shop line had expired. But I might be mistaken and they were produced side by side for a while.