Hi, yes I'd have no confidence the Moses writings are complete. A text called the "Assumption of Moses" depicts the last days of the prophet. It's regarded as 'apocryphal' though apparently cited in Jude 1:9. A fragment was discovered in Latin in Milan and published in 1891, alas key sections are missing.

The newly-discovered fragment has two quotations from "Jason & Papiscus." Here is the first one that touches on Creation:

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Papiscus said, “I would like to learn for what cause you honor the first day after the Sabbath.” Jason answered, “In this way, God commanded this through Moses, saying: ‘Behold! I am making the last things just as the first!’ The last is the Sabbath, but day one after the Sabbath is first, for on it, by the word of God, the beginning of the entire universe took place, as also the scripture of Moses declares, just as God spoke, ‘let there be light and there was light.’ The Logos which came forth from God and made the light was Christ, the son of God through whom all things came to be.”