And Hermoine and McGonagall too Mistress Siana! I could never really consider either of those two going to the dark side either!
As for why Snape wouldn't know... I really dont' think that Voldie was that trusting of a guy that he would have told all of his DE's everything. Actually, I don't think that he would have told any of them absolutely everything. He just seems like that devious kind of guy... even the type of person who would play his followers off eachother to rate their loyalty to him!
So yes, I would think that there is stuff that Snape doesn't know!
Also, what if Voldie has also thought about the possibility of some of his DE's either changing sides or being spys? Another reason I don't think that any of them would know absolutely everything! After all, how can you tell the other side about things you don't know???
