At the end of the War of Power, Lews Therin Telamon led the Companions to seal away the Dark One. By luck or design, they caught the entirety of the inner circle of the Forsaken there and sealed them away, too, shattering the forces of the Shadow.
How, then, was Ishamael still able to visit Lews Therin afterwards and grant him the moment of sanity and name him Kinslayer? How was he able to masquerade as the Dark One over the three thousand years between the War of Power and the present day? Is this ever explained?