Don Salzar, the watcher who was killed by Kalas, and was Methos's mentor, I'm not able to help but to wonder if he knew that Methos was "the Methos?" I would almost think so, because they shared a lot, and as he was dying, when Duncan found him, he was trying to write Methos's name in blood. Maybe Methos made him promise not to say anything to the other watchers.