How doesn't he know though? I realize cell phones don't exist but they can't send a raven? Something? A Night's Watch infiltrating your team seems like it would be at the top of the list of information to relay to Mance Rayder.
Then again I'm kinda fuzzy on the distances between the Wall and where Mance is, so I guess it's possible.
Fred.
The only people who knew were the wildling team that scaled the wall and attacked from the south side of the wall (ygritte and her boys). They didnt have any way to contact Mance on the other side of the wall this whole time.
What im wondering is how did they know to attack castle black at the same time as Mance's army on the other side did as well? Did they hear the horns too?