Fourth Age Past Lives

[Thalia]

Soul/thread thing. They are bound to the Wheel as well as the Horn. Birgitte was afraid Moggy ripping her out of TAR had broken it for her, but even that didn't do it.

New Heroes could find themselves bound so as well, men and women whose bravery and accomplishments raised them far above the ordinary, but once bound, it was forever.

- The Fires of Heaven, Meetings

Mat was told he had done more than enough to become a hero of the horn, but had not been chosen, which suggests some unknown criteria beyond deed. Presumably the Pattern lol. So they may "earn" their spots through deeds in life, but I think their souls are already marked for it - they are spun out with purpose. So, someone can go down in history as a hero and not be bound to the horn. It doesn't make their heroism any less, just means they weren't required by the pattern to do it.

Heroes don't recognise each other when they're reborn, but they do when they reside in TAR between lives. So their souls aren't treated as ordinary even between lives.