Why Would Elohim Leave Progeny of Adam No Record of History for 2,500 Years Until Time of Moses Toledoth Proves Did?

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If the record of the global flood were not written down by Noah on clay tablets or stone, rather first written by Moses on papyrus or skins a thousand years later, then from whom did Moses get the idea that a cataclysmic flood had covered the earth, from the legends of the Akkadians (Assyrians) and the Sumerians (Kushites of Kish) whose accounts though lacked the detail of the apparent eyewitness account and were absurd in the brevity of the flood which covered the earth? All but the six days of creation in Genesis was recorded by eyewitnesses, “these are the generations of . . . . (fill in the blank beginning with Adam, then ten more times in Genesis) meaning these are the origins of . . . .