Deep space 9 screwed up the whole thing by haveing Kang, Kor, and Koloth appear as turtle heads in thier episodes while maintaining that the Original TOS klingons were swarthy as well in thier Trouble with Tribbles tribute.
Roddenberry always maintianed that just as the movie’s credits say: the movies are “based on Star Trek” and therefor the kilingons had ALWAYS been turtle heads. AKA TMP was a reboot of the series and just like George Lucas he made the movie Klingons to make up for what he had always wanted to do with them. it makes NO sense that the fedeartion and educated starfleet officers 80 years later wouldn’t all know the story of how three years after the end of the 5 year mission ( as Obrian and even Bashier had no clue of the switch) the chief enemy of the federation simply appeared to have done a complete metemorphisis. Like this was something that starfleet’s finest had never even heard of and Worf wouldn’t speak of it. Just stupid.
Enterprise had to come up with a silly explanation at that point. DS9 just f’cked us in the a$$ on that one!