4k77, 4k80, and 4k83 are 4k (hence the name) versions of Star Wars, The Empire Strikes Back, and Return of the Jedi, respectively. 4k77 was mastered from an original 1977 35mm print of the movie. I'm not sure of the other's sources, but they're probably similar.

Despecialized are sub-720p edits based mostly on the Blu Ray 2011 release of the original cuts, with some parts sourced from LaserDisc, DVD, film reels and original matte paintings. It's a work of love that took the HD Blu Ray version and video-edited frame by frame it to look like the original release. It's a much better watch than the special editions rips, even though those rips have better resolution.

The 4k editions are high resolution scans from original film reels, they are typically found as 1080p and 4K.

If you don't mind 25-50 GB per movie then the 4k are the way to go, otherwise get the despecialized (they're under 2GB).

83's been done. It's just 4K80 that's still in beta. They finally released a 4K one (previously it was only available as a 1080p edit) but the color correction isn't yet done all the way to the end

From what I can find, Plex downloads subs from opensubtitles.org and they already exist there. I think the problem is that it treats "Star Wars" and "Star Wars Despecialized Edition" as the same movie

It seems like the file is too large for the clipboard, so it only copies the first ~20kB out of the total 100kB. I could probably find some workaround, but it seems like the despecialized subs are already available at opensubtitles.org, though perhaps a little bit hard to find. See my other comment.

I had a look and it already has subs for the despecialized editions, however they seem to be mixed in with the other versions of the movie, making them a little tricky to find: https://www.opensubtitles.org/en/search/sublanguageid-all/idmovie-458

Maybe there's an easier method, but I filtered by language and then used the browser's "find in page..." to locate the ones with "despecialized" tags

I put all the subs in a zip file, in case anyone finds that easier than hunting them down individually on opensubtitles: https://www.swisstransfer.com/d/2ab10863-e9f9-442b-9d2c-44f0711f8280

Max validity was 30 days, so if someone has the possibility host them more permanently others might appreciate it in the future.

The only info I have about the actual video files is that Star Wars is supposedly Despecilized Edition v2.5, while ESB and RotJ only come with a text file crediting Harmy. Perhaps the latter two are also v2.5 but I have no note of it.