
Gee, ya think!? "Fools" doesn't even begin to describe you...
There's also SW: Legacy, where as I recall the Moff Council secretly collaborates with the One Sith to overthrow Emperor Roan Fel, and Grand Moff Morlish Veed is led to believe that he'll be the new Emperor...only for Darth Krayt to declare himself emperor and makes the Moff Council swear fealty to him.
At least Moff Calixte has enough common sense to lampshade this, as well as certain other things in secret...but I digress, another moment that comes to mind later in the comic is when Captain Yage gets fed up with serving the Sith after one too many atrocities and defects to Fel's Empire in Exile:

The Sith have no honor? You don't say, it's not like they haven't demonstrated this sort of thing for millennia or anything!
So is it possible there's a justification for this collective, galaxy-spanning Sith-specific amnesia? I mean besides the need to rehash the usual "Sith backstab, betray and wreck shit up in the galaxy" plot. Something similar to "The Shroud of the Dark Side," perhaps?