The past - concrete, or mutable? Options

The future is apparently mutable, meaning there are many possible paths that could be taken. Just because we "know" something happened in the past (like a past life, etc), does that necessarily mean it happened, or is just one of many possible pasts? It is common metaphysical doctrine that every event exists in the present moment, so does that necessitate that there is no concrete past?

Maybe I should clarify. If I were to obtain a memory of a past life from the Akashic Records, is there a difference between that construct, and say, a "made-up past" construct. Both are constructs, yes, but does the one that was obtained/remembered have more validity than one that was made up?
This may seem like a different version of the question "Is there inherant good and evil?", which in a sense, it is. Of course the answer to the above question is "no, good and evil are what you make of them". I'm wondering if the past is the same. Is it what you make of it, or do remembered pasts have more "validity"?
The question would not be raised were it not for all these books out there like "Remembering your past lives", etc. If the past is "merely" a construct, what use is it to do such a thing, as opposed to "inventing" some?

Note: I do agree that this question is pointless when one considers that there is no time, but I ask it out of curiousity. It is part of the greater question, "To what degree do we determine our reality?"

This post has been edited by Sadako: Oct 26 2005, 12:14 AM