I'll try to answer some of you questions to the best of my knowledge from what Steve has told me in the past.
I agree with you that I have seen some early TW1a's that still used the foam covers. Driver interchangeability is a guess.
Steve did not have anything to do with the KX series and I don't think he's a fan of horn loaded tweeters because it does not show up in any of his other designs. Although DCM could have made use of some of his technology in their later designs
Steve's connection with the company ended around 1999 when Mitek took over. His designs would include all of the TimeWindows including the SurroundScape, TimeFrames, Macrophone, TimePieces, HalfTime, FullTime Base, TripleTime, CX series, VLS-2, and possibly the OW-1, OW-2, and a few subs. DCM has been reusing some reincarnation of some of these names like the Time Frame Evolution which has nothing to do with Steve.
Steve told me that marketing wanted a floor standing version of the CX series. That's how the TimeFrames came about.
The screen does more that just hold the tweeter. It smoothes out the frequency response. I would guess that it is not need on the woofer because of the lower frequencies. A Japanese company made the poly cones special for DCM and the drivers were assembled with these cones by another vender. DCM then could change driver venders for assembly, but keep consistency in their speakers. According to Steve, these cones had a very flat response, and they were not locked into one driver vender. To show how good they were, that same 6.5 driver that was used in the CX and TimeFrame series was used in Steve's signature series TimeWindow Sevens that sold for $3,200.00 a pair in 1999.
I hope this helps, if anyone has anything to add, please do so.