I don't think it's fair to call it a blunder. When the current EU began with Heir to the Empire (I know it really "started" with Splinter of the Mind's Eye, followed by the Han Solo/Lando adventures), virtually nothing was known about the Sith save the lone mention of them as Vader's title in the A New Hope novelization. So if you were only a movie watcher and never read the book, you would have never heard the title of Sith until The Phantom Menance in 1999. What did the authors at the time have to work on, really? Vader nor Palpatine were ever referred to as Sith; Vader was simply a Lord of the Sith, which Zahn took to meant that he lorded over a group known as the Sith. His original intentions were to have the Noghri be the Sith, but IIRC Lucas or someone at Lucasfilms stopped him from doing so. Since the concept of Sith was entirely unknown, what to call the bad Jedi? It wasn't until Tales of the Jedi, shortly after HTTE, that the Sith began to be fleshed out. They were a species of non-humans who were dominated by fallen Jedi in the aftermath of a great Jedi war. These fallen Jedi became the Dark Lords of the Sith and eventually waged war against the Old Republic and the Jedi, but were annihilated. Naga Sadow, a Sith-Dark Jedi hybrid, survived and passed his teachings on to another fallen Jedi, Freedon Nadd, who eventually passed his teachings on to Exar Kun, another fallen Jedi, who created a group called the Brotherhood of Sith comprised of, yet again, fallen Jedi. So Sith were a species who were dominated by Dark Jedi, ruled by them and then eventually became used by fallen Jedi who pledged themselves to their ancient teachings. It wasn't until The Phantom Menace that we find out that Palpatine is a Sith, and all Sith refer to themselves as Darth (before it was simply Vader's first name). We get the backstory of the Sith being founded 2,000 BBY by a fallen, unnamed Jedi (Ruin), and eventually the Rule of Two by Bane, which put a wrench to all the EU so a retcon was devised out of the pre-existing Battle of Ruusan. It wasn't clean, but it was necessary. But even the movie doesn't imply that ALL dark side users are Sith. The Jedi Council is convinced that Maul is not a Sith, but Qui-Gon believes otherwise, because he's faced Maul in combat and knows that no mere darksider could be so powerful and skillful. It's only after Jinn is killed that the Council relents and accepts that the Sith have returned. If the Council immediately suspected the Sith returned simply because a Force user was waving a red lightsaber around then I could see your point more clearly. And not ALL dark siders were even referred to as Dark Jedi in the early EU. Palpatine was never referred to as a Dark Jedi, as far as I recall, merely a master of the dark side. The Dark Empire Sourcebook actually differentiates between Palpatine's Dark Jedi and his Dark Side Adepts - page 37 of the sourcebook has the passage "...This battle plan made use of all his resources - not simply COMPNOR or the military, but everything. This even included his Dark Side Adepts and Dark Jedi." Dark Side Adepts have their own section in the sourcebook, including the likes of Gwellib Ap-Llewff and Savuud Thimram. However, the sourcebook contradicts itself a bit on page 70, where it says that the Imperial Sovereign Protectors are trained in the Force by Senior Dark Side Adepts and are sometimes selected to become Dark Jedi themselves. So yeah, the EU was working with what they had at the time. Once it became known what the Sith really were, things changed and there have been many new Sith since. But Dark Jedi haven't vanished completely - Asajj Ventress and Aurra Sing come to mind right away. Krell, from the Clone Wars cartoon, can definitely be seen as a Dark Jedi. Or even any of the fallen Jedi during the Clone Wars who sided with Dooku. Fallen Jedi who went to the dark side.