Yes, all true and possible but ...
MOS designed tens (hundreds?) chips and this was its core biz.
I assume design artifacts were store is secure chambers and multiple places.
I also assume that when a company like this or Commodore is bought (and when was bought it was absolutely reasonable to think at evolutions of those chips or other chips still under development) one of the first things done during the due diligence is to deposit in a virtual secure chamber the IPs or at least proved reverence to how obtain them).
Another one, I think blueprint for PCBs, cases are archived on a similar way chips are. An these have been used for sure to produce the last slightly modified a1200. So ESCOM(?) Should have been exposed to such archives at some point.
Anyway, I hope people who know and have been involved in Amiga design or management, and still active in the Amiga scene, like Dave or Peter, could shed some light or be interested in finding how things went.