It is taken as a fact in many books and specialized publications that the Maya calendrical system - the Haab' and the Tzolk'in - was more accurate and closer to the real solar year than the Gregorian calendar (even though reputable sources claim it is 365 days compared to 365.2425 days). But how is this really so? In all the studies I've read there is just a description of the calendars but not how that accuracy is obtained. How's that?
Update (05/04/2018): I've found multiple resources that support the premise on which this question is asked. However, I do recognize the issue of finding a relevant primary source (such as a Maya stela or a given codex). There was a discussion on Wikipedia regarding Maya expert Coe disproving this premise, however, since this question was asked, the author of this other question has edited it saying that Mr. Coe includes no references that support his statement in a section the user found. The question remains open since I'd like to compile more sources from other users.