That begs the question of where did they get those good prints from if Lucas insists the films are in irreparable condition?

Lucas is just banking on the lack of knowledge among the public about how films are archived, handled, assembled and processed. Anyone who does even a little research into the topic will find out that an original negative is not the only source for a film.

In any case, they have the SE negatives with all the changes baked into them so its not impossible to imagine them rescanning those, chopping out the footage that contains SE changes, and then dropping in original version footage. Because these would all be realtively short isolated sections of footage they could pick and choose sections from any number of sources on a case by case basis to do this. This is how The Godfather was restored. They used as much original negative as they could but where it was too degraded they chose footage from other sources to fill in the blanks, in some cases going as far to rotoscope good footage into degraded scenes. The SE negative apart from the specific SE-altered scenes *is* basically a restored copy of the original.