The first book was five short stories, that were published separately over the course of a couple of years. The original published novel was those stories collected and revised.

But yeah, the story evolved as he wrote further novels, and the first one ended up being the most out-of-sync with the rest, so when he wrote the last three after his accident, he went back and revised it again to better fit the overall story.

He’d talked a bit about going back and revising the other books in the series once it was all done, but I doubt that’ll ever happen.

To use a Star Wars metaphor, it’d be like if the first movie was set in 3251, the Death Star blows up Earth, and the Emperor was two different people, but then Empire and Jedi were released afterward exactly as we have them now. So then George went back and removed the date references, changed the name Earth to Alderaan, and removed any references to there being two leaders of the Empire.

It’s not as dramatic as all that, mind you, but that’ll give you an idea of what sort of things were changed in the revised version of DT1.