But what if oral tradition never happened? Moses was trained as one of Pharoah's son's. It's entirely reasonable to believe that Moses could write. If God directed Moses to write the first five books of the Bible, then there is no oral retelling for thousands of years. There is only copying of the works of Moses and the obvious addition of the death of Moses.
Exodus 17:14 - And the LORD said unto Moses, Write this for a memorial in a book, and rehearse it in the ears of Joshua: for I will utterly put out the remembrance of Amalek from under heaven.