[CWBP2] Races

[Deadshade]

Why couldn't one tribe of humans be spawned from the shed scales of a world-circling dragon, another tribe the offspring of a pair of gods that fell down from the heavens, a third tribe arising from the verses of a poem given form in flesh? Such myths could even be all true simultaneously, since they'd apply to different parts of mankind.

Yes they could. But there are conditions :

1) It happened in a very far past. My grand grand mother certainly didn't spawn from a scale. Why ? Because she remembers her father and her mother and they were not scales.
2) The first spawn people didn't know how to write. If they did, they would probably have (at least) a genealogy of rulers. We know that Akenaton didn't spawn from a scale because the names of his parents were written down.
3) The present people are unable to date ruins, tombs, skeletons, sediments etc. If they do, they can either rule out a legend which is dated (like Adam was created 3000 years ago) or set a bound in time for the scale spawning.
4) Regardless of dragons and gods, the evolution works in parallel also on this world and would have produced independently intelligent species too. These latter must not have been witnesses of the scale spawning (or have no means to leave a message) because otherwise there would be a trace of such a surprising event - one day there is nothing and next day there are strange people that nobody has seen coming and who don't remember where they were before and who their parents are.

So like Azelor rightly said the people in the world have no means to know whether the legends that are necessarily situated in a very far past without traces and without witnesses are true or not.
Only we can know because our memory extends far beyond theirs. For all practical purposes all their legends could be wrong if we decide so. But that wouldn't stop the people creating and believing them.