For reasons unknown, even comparing the 1982 NTSC VHS and LD in Fullscreen (which you would expect to be the same), the films are different. Different sizing, different pans and different scans. There are many times when different charachters are on the screen at the same point in the film.
Undoubtedly, there were even more differences for the THX releases but differences were there way back in '82.
Anyone who got hold of the 1982 releases by The Starkiller from a.b.starwars can easily check these differences out.
There is of course the 1977 bootleg to compare with as well along with the US premier (if anyone ever gets around to capturing their VHS) and the 1982 PAL LD when that is captured and released.