Empire Strikes Back had two original versions that I know of. A 35mm version that was more widely seen and a 70mm version with a good dose of small differences. The 70mm version is where Luke says "You're lucky to get out of there" to R2 on Dagobah instead of "You're lucky you don't taste very good." Also Luke thanks 3PO for his concern after Luke's recovered from his Hoth wampa experience.
The question I have is which version was made first? Also did either version come out after the film was first released (like the mono did for Star Wars)? And was either version considered more definitive? (On my mono thread somebody said the mono was considered definitive for Star Wars. I'm wondering if there was any comparable preference in ESB).
(If you want a good list of the differences the 70mm had from the 35mm you can look at the Wookieepedia Star Wars wikia article on List of changes in Star Wars re-releases, in the Changes to the Original Trilogy section. http://starwars.wikia.com/wiki/List_of_changes_in_Star_Wars_re-releases )
I think the 70mm was used as the basis for the SE version.