On the Mayan Calendar subject, one thing that I think should be mentioned in all of this is that most of the Mayan written history was destroyed by the Spaniards. Most writings were burned (primarily by priests and monks, who thought they were the work of the devil) so that only three authentic Mayan Codices survived also with a few fragments of others (note: there are some claims that more exist, but those are all disputed). Those few Codices, along with whatever is written on walls and surviving pottery fragments, is all we now have. With such a massive loss of information, what we know about the Mayan culture (including their calendar system) would likely be incomplete.
I have heard they had a cure for cancer, which was lost during this period. And since I just said that, I am sure it is, in fact, true and not some episode of The Twilight Zone or a book by Michael Moorcock.
Yeah, it's funny to look at all the stuff that was speculated, before the Mayan hieroglyphs were deciphered, on what they said. It was usually speculated that the writings said advanced stuff and had deep knowledge about the world and the universe. Then the writing was eventually figured out and it was all just incredible mundane stuff and a lot of ancient superstitions.
It makes me think there must be (or should be) a logical fallacy named just for this, the assumption that any ancient mysterious (or even mythical) civilization must have been more advanced than our modern day civilization. It's like some sort of "Paradise Lost" fallacy.