Using the “I heard it from hairy_hen therefore it’s gospel” standard, and hoping I don’t misrepresent what he said, here’s the scoop:

Star Wars was the only film that got a new mix in 1985. Any slight differences people have heard on 1985 Empire releases for example are consistent with the normal variations that can happen when creating a new release using the same audio master.

1993 was a whole new master, but Star Wars was the only film that got intentional content changes, and Empire got an accidental change. Jedi has no content differences. The Empire change was a missing snowspeeder crash sound effect.

Empire’s mono mix can be heard on Puggo Strikes Back or the most recent Despecialized Edition. They’re both from the same 16mm source, and there are a few content differences, as well as a number of clear mixing/levels differences. Basically, C-3PO gets a few more lines. It’s worth a listen, just for the historical curiosity alone.