The first film uses the same transfer as the Special Widescreen Edition, 1993 Technidisc pressing. (In fact, I believe it first appeared on VHS, before the LD repressing.)
Empire and Jedi, AFAIK, match the SWE discs, including Jedi's letterboxing still being shifted up like the Japanese Special Collection.
As for PAL, the pre-THX PAL widescreen transfers are confusing. The French/German widescreen LDs seem to use a different source element than the NTSC JSC/SWE transfer. I know that unlike the JSC/SWE, the French and German releases switched to an awful, dark, faded, grainy dupe for the subtitle-less Greedo scene.
The 1991 UK widescreen tapes, however, seem to be converted from the NTSC widescreen transfers seen on the JSC/SWE discs. The weird yellow-green hues in that Empire frame are evidence of this. And as Russ said waaaaay back in 2005:
For some bizarre reason, the 1991 Trilogy Special Widescreen Edition films are approx 4% longer than the other releases I have.
Star Wars 118 mins and 122 mins
Empire 119 mins and 125 mins
Jedi 126 mins and 132 mins
It is almost as if there is some type of framerate compensation to make the films play for the same length of time as the same as the theatrical and NTSC versions.
It appears that he was right, and they just transferred the NTSC versions to PAL. I would bet that the first film even has the "shrinking ratio" problem.
In comparison, it would seem that that the later UK widescreen tapes used the "PAL GOUT" transfers seen on the French "Coffret Trilogie" LD set.