When reading this kind of literature, you have to engage in "the willing suspension of disbelief", and accept things like magic and dragons that do not occur in our world.
In our world, prophecy is bullshit. Pure wishfaul thinking. There's never been a provable case of it. As was pointed out, Nostradamus was so vague that people selectively interpreted later events to fit them into his framework. And how many times has history rolled right past the end of the world as predicted by some doomsayer's interpretation of religious prophecy?
In Randland, Prophecy works, and it works however Jordan and Sanderson choose. The reader just goes with it. It's OK to point out internal inconsistencies, but if an author posits prophecy, its manner of fulfillment is up to him or her. I think WoT made a great point with the way prophecies were revised to manipulate the Seanchan. Give a nation an excuse to believe it's their destiny to conquer the world, and they'll go out and do it. Prophecy, like religion, is a great manipulation tool because you can't debate something that has no basis in logic.