A careful review of all the different releases and comparing them to the timeline shows that the original May 1977 version of the film (see Moth3r’s bootleg and Puggo Grand) had 4 differences. 3 FX shots and the end credits. Not to mention the soundtrack.
I’m curious, which FX shots are replacements?
When the Falcon leaves Tatooine, the shot of the Star Destroyer shooting at it, then the composite shot of the Yavin IV temple when Leia et al arrive, and then the shot with the Rebel lookout when the Rebel fighters blast off. There are subtle differences between those shots in Moth3r’s bootleg, Puggo Grand, JSC, and SWE and those same shots in Definitive Collection, Faces, GOUT, SSE, 4K77, and all the non-English versions (German, Spanish, and French specifically). Two of the were changed for the SE. Because SSE, 4K77 and all the non-English versions (even the earliest pan&scan releases) match the Definitive Collection and GOUT, the change had to be made for the late 77 release and they must have used a modified copy of the May 1977 edit for the early English language home video releases which would explain the JSC and SWE. But thanks to them we have them in widescreen. They aren’t too noticeable upscaled to 720p and spliced into 4K77.
I’m not sure if those shots are actually different. Having captured the 16mm myself for PG (and PE), I can say there are many ways I could have captured it, which would have led to differences is appearance. The one and only proven shot difference that any of my 16mm captures uncovered was in ESB when Luke was rescued from Cloud City. That caused a bit of a stir, I might add.