The root of this thread is a comment about "not contradicting yourself too much" yet there are a couple of comments within the thread that seem to imply that because we can find some examples of contradiction in fiction then uncontrolled/unlimited contradiction should be fine. This "I can think of a counterexample - let's make it a rule" seems to appear more frequently now but maybe that's just me.

The Star Wars Mitochondria revelation was unpopular, but it didn't contradict anything. The original movies never address whether you could detect force users with a blood test.

People working with definitions of words that the experts in the field don't share isn't the sort of contradiction being discussed. Things like the location of towns, how physics works, history of a place. These are things that are expected to stay consistent, and when that expectation is broken, it needs to be handled with care. History being uncertain is one thing, but the author directly stating that history is X happened before Y and later in the story stating that Y happened before X creates a problem. If the author is purposefully going for an unreliable narrator or implying that history literally changed then that can work (if the author has the skill to pull it off), but having it change because the author forgot to stay consistent is quite immersion breaking and creates an issue of an unreliable author, which is much worse than an unreliable narrator. Can a language model keep straight things like "Kingdom M thinks X happened before Y" vs "X happened before Y"? Even humans commonly make mistakes with things like this.

These aren't the sort of contradictions you care about in a literary or role-playing fantasy world. Players typically cut you a lot of slack when it comes to economics and ecology.

But they do care about what you've said. If you told your players that all magic comes from the sun, those creatures from the deepest caverns better not have any magic. You can make up excuses as you go along, but they will think you a worse GM for it.

If they draw an inference that was valid from what you'd said, ("Hagrid said every single wizard who had gone bad was in Slytherin. At the time he said it, everyone thought Sirius Black had gone very bad indeed. Ergo, Sirius Black must have been in Slytherin! See, they can be good!"), that's annoying in a book, but in a role playing game it's downright frustrating.