Maul was Sidious' apprentice up to the point that he was killed. Keep in mind that Labyrinth of Evil takes place about 13 years after The Phantom Menace. Dooku became the apprentice Sith after Maul was killed. As far as I know, the complete story/truth of Syfo Dyus has not, yet, been revealed. I think that will play a part of Episode III. If more has been stated, I'd like to know, too.