You can destroy the negatives with extra processing but you can't destroy the prints. Lucas has original prints and if he didn't he had the millions to acquire them. If fans did it, Lucas could have.
The rumor I heard decades ago (so a mountain-sized grain of salt) was that he didn't want to admit he fucked up the originals when making the specialized editions, and just acted like he didn't want to release remastered theatrical versions. He was also fiercely defensive of the specialized versions, saying that they were closer to his "vision" than the originals.
Master negatives can create higher resolutions than what you get from the prints. The fan-made versions did a ton of upscaling from the best quality digital versions they could find.
The negative is 35mm like the print. There is technically a generational loss between negative and print but that's far far below the resolution of a 480p DVD when Lucas claimed he couldn't release the original. 35mm film print is higher resolution than 4k. The 4k77 version does not use upscaling.
Lucas had just re-released the Specialized editions in the theaters, and they did very well. There's no way they go through the effort of remastering the originals without releasing them to theaters.
I don't remember where exactly I found it, but search for "Phantom Menace Anti-Cheese fanedit" or some variation thereof. I originally found the full thing on Youtube, but I would not be surprised if it has been taken down. That was many years ago.
In hindsight, all of media used to have this "meh, close enough" attitude about it: Vinyl LPs, audiotape, broadcast TV, film, iffy projectors at the local theater, AM radio, it all had limitations well within the range of human perception. Plus, everything the consumer got was a lossy copy of something else. Everything had noise, and everything cost some amount of fidelity no matter what you did. In light of this, "authenticity" is really a No True Scotsman argument, where we argue forever about intent, the optimal fidelity for the time, and what one would have experienced.
Come to think of it, an easy approximation for a time machine is to buy some aviator frames, smear some Vasaline on the lenses, and stuff your ears with some cotton.
In light of this, "authenticity" is really a No True Scotsman argument,
4k77 isn't a no true Scotsman because it is a scan of a print that was played in theaters. If you digitally scanned a photo of the Mona Lisa, it would be a more authentic copy than a Photoshopped version that removed the brush strokes and replaced the blurred background with new high detailed images.
smear some Vasaline on the lenses, and stuff your ears with some cotton.
Had you watched movies in theaters before 2013? Film projectors were fine. The sound quality was fine. A movie filmed and projected in 35mm film was higher quality than the 1080p digital version of Phantom that was in theaters in 1999.