So you are assuming that they should expect (or assume) him to be aware of the time of Dyas's death even after he conveyed the message that he believes Dyas to have been dead before the order was placed. Then replace Yoda with Mace as he ultimately agreed with Yoda at the funeral and with Mundi at the temple. To the movies, Maul is a true Sith Lord. That will not change. To the EU 13 years later, he isn't a "true sith." In another 13 years, something else will be completely different in the EU for various reasons and motivations. It's a contradiction to the rule when 13 years later you decide Maul isn't a "true sith." As far as the films go, there wasn't sufficient evidence for Yoda to make that claim at the time he did. He made an assumption. Someone could have just as easily turned to him and said "do not assume anything, Master Yoda, if you want to find the real villains behind this plot." At least he didn't get the Obi-Wan treatment with him turning and saying "only a Sith deals in absolutes" while glaring at the little green guy. I guess that's the end of that point of discussion. No. But they also are not required to complete their training into creatively thinking warriors.