Here's a point but not proof indicating that two people cannot exist at the same time. That is one of the current characters (Mat, Olver, etc) could not be one of the heros called at Falme when the horn was blown. People have suggested that Mat could be Artur Hawkwing and cite time differences between the real world and TAR for both Hawkwing and Mat being at Falme. Well if that is true, then why didn't LTT show up when the heros were called? And why did Hawkwing call Rand LTT but didn't recognize himself in Mat? As I say, it's not proof but it sure is convincing for me!