When there were hundreds of cultures and languages.
Imagine a "European code of ethics" from 1715 that included Basques and Sardinians, Poles and Jews and Russians and Scots and Greeks and Turks and Serbs and Hungarians and Irish and Tatars and ...
Esp. if there was no means of writing most of the languages involved or recording anything apart from oral tradition. Sometimes oral tradition preserves things for 1000 years; sometimes the narratives get thoroughly rewritten and adapted to new circumstances in less than 100. But since there's no direct way to check which is which, you're stuck looking at how archaic the language is in the traditions. Zuni, pretty old. Most of the rest? Hard to say.
This, when there were still some cultural displacements going on (can't forget the Sioux or the Apaches) using military means, and 100 years or so after a series of devasting plagues must have ravaged the Native American tribal population and devastated their social orders, while additional European species and technologies--pigs and horses, for example, plus more metal--had to have some effect.
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