Not necessarily true. We have enough information on Mesoamerica we can built an extremely complicated political map. You can refer back to the efforts of Mesoamerica Universalis on this score. A friend of mine also, sometime ago, did a map based upon contemporary research on the Mesoamerican Postclassical at the end of the Tepanec ascendancy and the collapse of Mayapan (for the sake of a forum game you can find
here). Creating a similar map for 1337 would be challenging and complicated, but not necessarily impossible. And the advantage of historical cartography is once you've developed a map that shape stays until you improve it. Paradox can over time iterate and improve their Americas representation until it reaches a similar level of fidelity.
(To be clear, I think a lot of these tags would be merged on the actual map for EU5, but it's an example of how this task is *not* impossible).
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