Dear readers.
People lie.
Fey lie (a lot).
The Fae don't lie, they always speak the truth. What the listener hears and understands however, is not necessarily what the Fae says.
Pages get translated poorly.
People lie.
Libraries burn and librarians rewrite them from memory.
People lie.
People lie.
People lie.
From a historical standpoint, most of the copyists from the first several centuries, really from before the beginning of the Dark Ages until well into the Renaissance era, were illiterate. The copyists would just reproduce the shapes of the letters on the scrolls and books that they were tasked to copy, they typically had little or no ability to read what was in front of them, never mind edit or make changes. However, many of the stories with which we are familiar were part of oral traditions, and as such had most likely been first told centuries before they were ever written down.
Consider for instance, the Celtic/Druidic traditions which were passed along orally. Or the Norse skalds. The greatest bodies of writing detailing Norse legends, the Prose Edda and the Poetic Edda, was actually written in Iceland in the 13th century. The Poetic Edda was really more a written collection of traditional poetry from earlier periods. Keep in mind also that Iceland was first colonized late in the ninth century. The closest equivalent to that would be for stories regarding the first settling of the New World, stories like that of the First Thanksgiving and Pochohantas to be past along as an oral tradition without being written down until 1965.