Oh, you'd be surprised. Lucas was quite a pack rat, and Lucasfilm has a full-time archivist that has every surviving print, mag track, photograph, script, outtake, costume, prop, and everything else that survives. For example: I just learned that since director Rian Johnson was loathe to use CGI for Yoda in Last Jedi, they took the original 1983 Yoda puppet out of the archives, had it scanned and a mold made from it, and made a precision copy of it, which they used (under Frank Oz's supervision) for the new movie. So every shot of Yoda in the new film is a rubber Muppet, not CG. And it's all Frank Oz's voice. They also worked very hard to get the color and texture of him exactly right, to follow the look of the previous films. I have rebuilt and reconformed old films before, and it's quite a chore. For example, I had to match all the split-screens, dissolves, and optical fades in Phantom of the Paradise for Fox, and it took days and days of work to get the negatives to precisely match the print, since we had A/B roll negatives. (I was part of the same process with Dances with Wolves, Star Wars, and Return of the Jedi as well.) It's a lot of work, but you can get it absolutely pixel-perfect if you work hard at it.