Is the Plagueis > All Sith Lords Before Him Blurb Indisputably Canon?
The question is the title: Is the Plagueis > All Sith Lords before him blurb from the back of the Plagueis novel indisputably a canon fact (in the Legends continuity, more so for the purposes of this thread)? If you don't believe that it is, what is the argument against it being canonical fact?