That’s like saying the FO rising or Palpatine returning is an off-screen history. And my example is still a contradiction. That’s my point.
Well, yes, it is an offscreen history. There’s nothing inherently bad about that. The problem is when it doesn’t make sense with preestablished story. The original Star Wars was its own story, starting from scratch, so it could establish whatever sort of history it wanted. The ST is beholden to the preestablished lore, and should be logically consistent.
Also, that’s not what a contradiction is. If we were told incompatible information about the Empire and Republic, then yes, that would be a contradiction. Historical change, however, is not a contradiction.