Re: tobi isnt madara, a clue
This has already been stated many times since Madara released himself. One explanation is that Tobi knew more than he was letting on or only knew certain things about Edo. Another explanation is that Tobi is part Madara with only part of his memories. If that is the case, he might know some things that Madara knew, but not everything.
One final possibility is that Madara discovered the secret hand signs sometime AFTER tobi was created. If that were the case, Tobi might not have been told the secret before Madara officially died.