mysycamore said:
... maybe new 70mm prints with the revisions were made for the US re-releases if not for the foreign markets in '80.
It's difficult to tell without a video of the original 70mm, but perhaps new 70mm prints were struck of reels 1 and 6 (which incorporated changes to Wampa cave, Luke and Vader telepathy and Lando's departure) to switch out with existing prints, rather than strike entirely new (and expensive) 70mm prints as the film opened wider, if other major changes weren't made.
That could also explain why the Luke/Wampa cave 70mm cell exists.