The most galling thing, I think, is that all the 2004 changes etc are made on a 1080p master! I really cannot fathom why GL, a billionaire many times over, didn't go with a 4K or 8K transfer for his most important films! Even the SEs had the advantage of a 2K transfer for the scenes that were augmented, apparently - and that was back in 1997!
The problems are summarized by Michael Kaminski, author of "The Secret History of Star Wars", here:
http://secrethistoryofstarwars.com/savingstarwars.html