I think the O-neg has a larger image field than what we usually see - framing around the edges is not always the same on every print or every video transfer (like the scene with the Tusken scouts, where in one transfer - JSC? - we can see a sliver of sky at the top that we usually don't). Maybe they just framed it a little farther to the left when they did the restoration.

If the IPs used for the THX transfers were dupes, then yes, the PAL could have used a different dupe.

It really baffles me how they wanted a source with a closer generation, but the prints they used may well have been more generations removed than the ones used for 80s video releases. Yet everyone back in the 90s, myself included, saw them as looking superior to the old releases - was it just due to the improved video mastering? (DVNR aside, of course...)