INAH's authority was tested directly by the Maya Codex of Mexico, formerly known as the Grolier Codex, which surfaced privately in the 1960s under circumstances that left its authenticity disputed for roughly four decades: critics argued a modern forger with knowledge of the three long-accepted Maya codices could have assembled a plausible fourth, while defenders pointed to radiocarbon dating of its bark paper and pigment analysis consistent with a genuine pre-Columbian date. As the country's official authority on Mexican antiquities, INAH conducted its own extended technical study and formally authenticated the codex in 2018, a ruling that carried institutional weight precisely because it came from the national body responsible for such determinations rather than from an interested private owner or a single outside academic.
This authenticating role sits alongside INAH's more straightforward custodianship of excavated material such as the Sun Stone and the Coyolxauhqui Stone, whose Mexica origin has never been seriously disputed, and illustrates a distinction worth holding onto: for some of INAH's holdings the institute is simply the excavating authority that took possession of a find, while for others, like the codex, it has additionally had to act as an evaluating body settling a genuine question of fraud, a role most museums in this atlas are never asked to perform for their own collections.