If I'm not mistaken, doesn't the presentation of the ATB suppose that it was probably written by Hobbits (most specifically, Bilbo and possibly Frodo)? While they were both more learned in Elvish lore than other Hobbits, there was much I'm sure they didn't know. Not to mention Bilbo's fondness for poetry, which often leans one in the direction of what sounds good rather than what presents an accurate picture of historical fact. It's not much to go on, alas. What is fact, what is fantasy? Enquiring minds want to know, but may never have an answer.