I'm damndably sure Darth Bane's story was created before KOTOR's. The creaters of KOTOR just put Darth in Revan and Malak's name 'cause it's appropriate 'cause they're Sith Lords and it sounds cooler than just callin 'em Malak and Revan all the time. Also, the creaters probably don't give a f*ck if it does screw up the histroy of the term Darth, 'cause they're only interested in finishing the game and sapping as much money from the public as possible.
Now if you don't mind, I'm gonna go toke up, buy a shotgun and shoot another hole in some Paki guy's ass.