Star Wars is notable for how poorly the original elements of the film have fared. For one, the film negative had severe problems with fading which made it difficult to restore even in 1997, and it has only faded more since then. There is also the fragility of the negative - certain parts were lost when subjected to the cleaning process.
To expound on that for the curious:
Tanaka: I remember when we were working on the Star Wars restoration, that was a different process. I think we optically recreated interpositives. But in order to do this, it went through some kind of warm chemical bath cleansing. The weird thing about Star Wars was that it was made up of different film stocks, so it went through this bath and they didn’t know what would come out on the other end…
Parker: You mean if it would survive or not? ‘George we might destroy your entire film, but it’s… we think it’s going to be OK.’
Tanaka: There’s a space battle shot and a close-up on Hans Solo, and the original negative is coming out of this cleaning solution and it’s just acetate.
Parker: It’s all clear. Oh no, did the bath dissolve it?
Tanaka: Yeah, it dissolved it, depending on the film stock.