Everything I have seen says that for Star Wars the 70mm and 35mm stereo tracks had the same 4 track master. No differences have ever been reported except for the two LFE channels that rounded out the 70mm’s 6 tracks. So it wasn’t specific to the 70mm. The 85 mix is identical to the 77 mix except for Threepio’s extra line. The 93 version has the same base, but more additions.

For TESB, the 70mm version was done before the movie was really finished. That makes 2 movies in a row like that, though for Star Wars they didn’t change the 4/4.2 track masters… they created a mono mix instead. So the finished audio is the 4 track master used for the 35 mm release. This was the first time a lot of these edits had been heard outside the mono mix. There was nothing new and plenty of omissions. I have no knowledge of the ROTJ 70mm presentation.

To achieve a proper mix, the new edits would have at least had to be added to the 4 track masters and then rematrixed. From a topic that came up a number of months back relating to the 1985 CBS/Fox release, it is not a difficult thing to rematrix the audio from the 4 track masters.