Check out Genesis 36:31 - "Now these are the kings who reigned inthe land of Edom before a king reigned over the Children ofIsrael."
A statement like that necessarily implies that there were kings which had already reigned over Israel before the time of writing. It makes no sense to place events in time by referring it to events which haven't occurred yet. In fact, this way of writing seems like a very typical way of referring to events which happened long ago.
Of course, if you believe in prophecy and all that then there's no problem pushing back the writing of the Bible back as far as you want. But it must have been strange for those guys wondering when those kings would show up.