I can tell you for sure that the 4K77 project does not have access to the master tapes or copies thereof.
Mike Verta hinted in one of his videos that he has access to them for Legacy, but for obvious reasons he couldn’t discuss where or how he got them, nor could he share them. But since he does work in Hollywood, in the film industry and did interview many of the people involved in making Star Wars, visited the Lucasfilm archives, etc. I don’t have any reason to doubt him.
I did read MV’s post about getting some official support from Lucasfilm, but didn’t know whether that included audio.
Hopefully, he treats the audio the same way he’s handling the video, except not using audio noise reduction (that will lose fidelity for sure).
Actually, (and as i noted in the OP), the LDs from 1993/95 were pretty good and lossless. I have no problem in Legacy/4k77 re-using that source for audio.