If I’m not mistaken, in Malachim Beis, there was a period where the Torah was forgotten until it was rediscovered and reintroduced back into the nation. If that’s true, that means that the Mesorah was severed, and for all theological purposes, one would consider the Torah to have originated from that one person in history. What happened prior to its rediscovery (i.e. national revelation) is immaterial, seeing as there was a window where only ONE person knew of it, and then subsequently passed it on.