Written vs. Oral Language

So far, this reading has blown my mind to an extent.  That is to say that I hadn't given a single CPU cycle to the concept of what it is to recall information in an oral society versus what we take for granted in a written language society.

This gives me quite a bit of food for thought and has actually raised more questions (to be answered later in class?) than I have answers for.  For example, if oral tradition relies on patterns of stories and memorization to recontruct history, and we learned that they often never tell the same story the same way twice, how is it even remotely possibly for their history to be true?

This is troubling to me in many ways because we tend to have an idea of ancient history which comes from these primarily oral societies.  Since we know that they often change the story or omit details that no longer suit their audience, are we to understand that what we currently know (or think we know) is merely the story that best fit the circumstances of their telling at the time written language was first introduced?