Aginor and Balthamel were sealed near the surface of the Bore, and as such aged immensely by the time of their release. After his release, Aginor attempted to control all of the One Power from the Eye of the World, there was an immense amount stored there, but he drained too much of it in a single time, so it was too much for hum to control and he was burned to ash. The green man killed Balthamel.
Ishamael (Ba' alzamon) was thought to only be partial sealed in the bore as he is able to touch the world and influence thing since the time the bore was sealed. The rest of the forsaken, besides these three, were believed to be freed at the same time.
It isn't that Rand can channel or is the Dragon reborn, as the seal on the bore was weakening and the pattern called for the dragon to be reborn to fight the dark one who would ultimately break out when all the seals(the thing in the eye with the horn and banner that was broken) are broken.