I looked again last night at the end of book one, and one of the two forsaken even mention that another, Ishamael, is also out and about. It just doesn't seem to make sense that after knowing that three are already out that afterwards everyone seems to forget this.

I remember reading somewhere that Ishamael is the one that apears on Rand's dreams, he presented himself as Ba'alzamon.

He appears in the prologue before Lews Therin killed himself, he is the one that removes the madness from the Dragon, just so he sees what he had done with his family.

Well, for what i understood, the two Forsaken, Rand and everyone faced on the end of Book One were both imprisioned in a layer closest to the surface, and were the first to be released, when the time of the return of the Dragon came.

I'm not entirely sure, as i'm in the second book, but maybe the coming of the Dragon Reborn and he beginning to channel, even without wanting to, may have been the trigger to release the forsaken, as they were imprisioned by male Aes Sedai. The kind of energy a male channeler used may have something to do with it.

Sorry if i'm mistaken friends :).