Think of it this way, the original negative is the master negative for creating all interpositives and presentation prints. It includes all composited effects, scene changes, and titles. For Star Wars/A New Hope, a 3 color separation master was also created which supposedly would let them create a duplicate of the original negative. For the SE, they went back to the camera negatives, the raw footage, to recomposite most (but not all) of the shots. I’m not sure to what extent they did this with the composited effects shots (which were all done in VistaVision so the final composite would not have increased film grain over non-effects shots) or whether they kept the original composited elements. In some cases the stars are obviously different, but in others they aren’t. The snow speeder sequences in TESB were all redone to correct a flaw with the way it was originally composited (that allowed the background to show through the darker areas of the image).
I often watch TCM in HD (720p) and a lot of the movies they show are from original prints with the cigarette burns intact. One was a restoration where the only complete version was 16 mm so the shots missing from the 35 mm copy were fuzzy. But at 720p, the scans of the original prints looks pretty good. The older technicolor prints often have some obvious misalignment, but a properly calibrated scan and subsequent filtering can separate and realigns the colors (Mike did this in a couple of shots - one scene he found several levels of misalignment and corrected them all because he couldn’t be sure of which were due to Technicolor and which were through some accident of production). Citizen Kane only exists as a high quality presentation print (the negative was lost long ago). For many old movies, the print is all we have and some of them are damaged. But I am often amazed at the quality. And some of the modern restorations are just incredible. About the only way to see the original 1977 Star Wars better than Mike is doing would be a full restoration of that 3 color separation. It has the same problem that a lot of old, pre-color negative technicolor films have, the negatives have shrunk unevenly. A problem in 1996 when GL wanted to use them to restore the faded negative, but not a problem today with digital technology that can realign the colors (this has been used in countless films, such as Gone With The Wind and a lot of early color negative films that were distributed in Technicolor that have the yellow too faded on the negative so they use that piece of the technicolor color separation). The restored ones are so much clearer, but even the unrestored ones scanned form original prints are pretty clear. And even Mike has commented that no all prints are created alike. He has seen one high quality one and one lower quality one (according to his comments). He’s also gone beyond just archiving and cleaning up the technicolor print to using algorithms to see through the grain and recover details, such as on the infamously low quality shot of Luke’s landspeeder passing through Mos Eisley.