There were many screw-ups in sith history, even before KOTOR:

1. Golden Age of the Sith and Fall of the Sith Empire are set way too long after the formation of the Republic and Jedi. 20,000 years of a Galactic Republic and hyperspace travel is still dangerous? C'mon.

2. Darth Bane should have been one of Exar Kun's followers. Did Lucas have to create another fallen Jedi incident?

3. Darth should absolutely not be a title. Darth being a title is like all Jedi being called "Ben (something)".