It seems clear from quite a few memories from Canada :-), that it wasn't just that the 70mm release was different to the 35 mm release but that there was for a very limited time a different cut 70mm version showing in a few cinemas before the final 70mm cut was released.

This does correspond to a quote I heard just the other day when watching one of the making of star wars documentaries, I am sure it was actually on the voice over from building empire, I will have to watch it again to check and get an exact quote and who said it etc. But the quote was from one the main special effect guys I am sure this was while working on the empire release he said the he was really annoyed with George Lucas because they had the film finished and then a few weeks before the final release the got him in again to do more work on the film because they had decided to change a few things.

Will post a proper quote when I find it.

WM