That's right. Dave Morgan's in-theater recording shows only minimal differences from the standard mix. msycamore listed them at the beginning of this thread. The 70mm mix was done before the standard 35mm mix, but the changes in the SE seem to be based on decisions made by Burtt and/or Lucas *after* the 35mm version was finished.

Some of the changes were already in place on the "Story of" LP and/or the Super 8 digests. The 8mm soundtrack even has Chewie roaring as he strangles Lando, drowning out Leia saying "...that we're going to trust you?", just like the SE. If there had been a revised mono mix of ESB like there was for the first film, I think there's a good chance it would have had some of the same changes as the SE mix.

Even though the 70mm cut was used as the picture element for the 8mm, it seems to me that the soundtrack was done *after* the 35mm mix. For example, although it only has the first Rebel fleet establishing shot (like in the 70mm version), you can hear the tracked "Yoda and the Force" music from the 35mm mix playing under the scene. Also, Lando's line "Luke, we're ready for takeoff" is the familiar take heard in the 35mm mix, not the alternate one that's in the 70mm mix.

Maybe Burtt and Lucas kept a running list of changes that they made/wanted to make to the mix? Even though there was no third complete mix of the film, the "Story of"/8mm differences are evidence that changes were still being made after the 35mm mix was locked, some of which were carried over into the SE mix 16 years later.