Notice that Methuselah and Lamech probably knew Adam himself, since they were family. They probably got the creation story first hand from Adam, since Adam was alive while Methuselah and Lamech was alive. Also, note that since Adam probably passed that information on to these two, and Noah was the grandson of Methuselah and soon of Lamech, these two probably passed the creation story down to Noah as well. That means the creation story was passed on directly to Noah's grandfather and father. So Noah learned of creation personally from people who actually knew Adam. Also, Noah probably passed this info down to his sons, Shem in this diagram. Even still, Shem probably heard it directly from Methuselah and Lamech also, since Shem was born and alive during the time of Methuselah and Lamach (again, who knew Adam personally). Shem was alive during the time when Abraham was alive. Notice that their timelines DO cross. It is a good possibility that Shem and Adam probably knew each other, and that Abraham probably heard the creation story from Shem. We know for sure that God spoke to Abraham anyway, from the Old Testament, so this was no surprise to Abraham. Abraham knew that God created all of this, and that Adam was the first man. That is probably why Abraham had a lot of faith in God, since he was spoken to by God, but also his other evidence was that Shem (who Abraham probably knew) knew two people that knew Adam personally. That would also mean that Abraham personally knew someone who survived the Flood (Shem). Notice also that Isaac (Abraham's son) also probably knew Shem personally, since their time alive also overlaps by at least 70 or so years.
If you think about this, Isaac knew Shem, who survived the Flood, and probably got the Creation story AND the Flood story directly from someone who survived the Flood and knew two people personally that KNEW Adam. That makes at least two people who got this information almost first hand.
With that said, look at when Moses was born. Not only Isaac, who got the Creation story and the Flood story from Shem, but Jacob and Joseph as well, who probably got the Creation story and Flood story from Isaac. That is very little time between Isaac, Jacob, and Joseph's death to Moses' birth and life. Don't you think that Moses would have mentioned what he knew was passed on to him? Well, we know that God did guide him in what to write down in the Torah. But he also knew these creation and flood facts because he was very close to the original people who heard and lived these truths. Just something to think about.
More thoughts on this theory: