In this case there is circumstantial evidence - from what I understand there is a huge difference in population estimates between the first time contact was mad

In this case there is circumstantial evidence - from what I understand there is a huge difference in population estimates between the first time contact was made with Europeans, and every time after that. All accounts point to an apocalypse due to diseases, even before the Spanish conquistadors came. In other words: it was the previous ground research that was at odds with the written accounts.