Example. In "Space Seed" Spock says WW3 and the Eugenics Wars of the early 1990s were one and the same thing. Yet in TNG it's rewritten as separate conflicts. From then on practically everybody goes with the explanation that Spock got it wrong and misremembered his history. Oh, and Kirk and McCoy happened to misremember theirs as well?---because they sure as hell didn't correct Spock. I don't think so. And this is but one of many outright and more subtle contradictions that piled up over the course of several films and spinoff series.
This particular example serves to show how retconning actually adds to the value of a scene. Obviously, Spock would get things wrong here, and obviously, the other heroes would not correct him, but at most snicker. After all, that's what had been going on for the past couple of minutes already! Kirk, Spock and McCoy all in turn "got it wrong" regarding the Botany Bay
, its history and occupants, and took friendly delight in the errors of the others.
Generally, I don't see why any particular story should be considered immune to later reinterpretation. It's all on the plus side: the original story survives, but new meaning is added to it.