When assembling the 5.1 audio for RotJ Despecialized v2.5, I noticed that the 1993 version for that film actually does contain two sound effects that are not present in the 1983 stereo mix.
The first is at the very beginning of the Dagobah scene, before it cuts to the interior of Yoda’s house: in the original mix, there is one sound of thunder in the distance, while the 1993 version has two.
The other added effect is at the end of the film, as the Millennium Falcon flies away from the exploding Death Star: in the original mix, the sound of the ship is heard in the front channels only, moving from center to right as it goes off-screen. The 1993 version has exactly the same front channel content, but adds the sound of the ship zooming into the rear channels as well.
I’m not sure exactly when these additional effects were introduced. Unlike the other two films, RotJ’s 1993 mix is not copied from an original master mix but was made from the separate stem recordings, so it is possible that these were present in the sound effects stems and not a deliberate change. Why then they would not be present in the 35mm stereo mix is unclear. Either they were added to the stems at the last minute and did not make it in time to be included in that version, or else they were present but deliberately muted. They might be in the 70mm version of Jedi, but since there is no copy of that available, there is no way to know.
More significant than either of these are some of the different mixing choices between the '83 and '93 versions. The '83 has the music consistently more prominent throughout most of the movie, especially when Han is unfrozen from carbonite and when Luke defeats Vader; although the '93 does have it louder in a few places, notably the Rancor scene and the Emperor’s arrival. There is some panned dialog in a couple spots in the original, but all dialog is completely centered in the remix. Finally, during the scene on Endor where Luke tells Leia how they are related, the sound of birds chirping is much more noticeable in the '93 remix. In the '83 stereo, it is present but quite subdued. Again, there is no way to know how it is in the 70mm version, although I expect that the 70mm resembles the 35mm more than the '93.
My version uses the 1993 for its dynamic range but I did insert the 35mm for Vader’s defeat, since the music sounds so much more glorious in that version. The unfreezing scene is still the '93, but increased in level during that section to make the music stand out more.
Good to know. That helps a lot. Sounds like for both TESB and ROTJ, there is the original theatrical and the 1993 mixes (plus the mono for TESB). I take it the 1985 mix for both films matches one of the other mixes and is extraneous.