um Doctor Who has had some huge retcons, the whole Timeless Child extra regens, the Time War and destruction of Galifrey etc. Entire seasons have been nothing but retcons-turned-plot.
This goes back to the argument about the difference between new information versus rewriting previous continuity when we're talking about retcons ("retroactive continuity").
The Timeless Child -- a storyline I will not otherwise defend -- was new information to the Doctor and the audience, although it colors our understanding of previous events. (That is, for those who don't try to block it out of their memories entirely.) Any long running story is almost always going to start presenting new information about the universe and back story of its characters, just by virtue of how many stories get told about them.
Compare to comics, where DC Comics rewrite the history of their universe any time they get bored, so that Wonder Woman was a founding member of the Justice Society, whoops, make that the Justice League, whoops, no, that was Black Canary, no wait, that was actually Wonder Woman, well, it was Wonder Woman's mom, no, it was Wonder Woman again, no, maybe it was actually Black Canary. That's not the characters being presented with new information, that's reality being rewritten. (In fact, in many cases, the characters of the DC Universe are not always aware of these changes and are, instead, victims of a rewritten reality that has "always" been that way, as far as they know.)
Which of these applies to the cartoon characters, who knows. It's probably just retcons but I guess there could be a more complicated story where they visited the Realm and it got merged into the Forgotten Realms (where were these characters during the Spellplague, hmm?) and then the world got separated back out again. But I doubt there's any such complex storyline sitting on a shelf somewhere at WotC.
