That's interesting to think about, but we simply don't know the answers to your questions, and there is no way of knowing for sure. It is even possible that Moses used writings by someone such as Noah, who could in turn have got the information from Methuselah. Methuselah talked with Adam and died either the year of the flood or 1 year before it. Almost certainly God gave Moses visions also. There is no reason to believe God worked with Moses in that sense much differently from the way He worked with Ellen White. She received visions, and then the Holy Spirit helped her in the writing and even in the selection of writings by other people. Likely it was similar with Moses. But again, it is all conjecture, and we will never know for certain until we get to heaven and can ask the writers themselves-- that is, if it still seems important to us at that time.
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Turning and turning in the widening gyre/ The falcon cannot hear the falconer;/ things fall apart; the center cannot hold; Mere anarchy is loosed upon the world... Surely some revelation is at hand;/Surely the Second Coming is at hand. W.B. Yeats