My understanding is the Library of Congress' print is an original. (No Episode IV.) The American Film Institute is supposed to have a print as well. Whether Empire or Jedi have been archived this way is anyone's guess. It wasn't a case of outright neglect of the film elements (as has happned to other films) it's that the film stock used was pretty lousy and not stable as time passed. It's not just family vacation photos that were screwed over by Kodak getting cheapo back then.
