So when it comes to Nintendo shipments US would be about 36m shipped, accounting for 85% of The Americas total. It seems too high if we think Nintendo's The Americas is more than Canada and the US.
Afaik, Mexico and Brazil are significant countries when it comes to shipments, and the rest of the Americas certainly add up too.
I'd put US shipments at about 35.5m, because sell-through passed 35m only one month later. The market size of Canada is roughly 10 percent of the USA, so that would be another ~3.5m. That leaves ~3m for Mexico and everything south of it.
Brazil has tax laws where consoles that aren't manufactured in Brazil will be heavily taxed, to the point that the black market with its imported consoles from the USA is able to offer much cheaper prices. Since Nintendo doesn't produce consoles in Brazil, the vast majority of the consoles in use there can be assumed to be US imports. This is why a ~85% share for the USA alone isn't too farfetched. Other South American countries don't tax as much as Brazil, but imported consoles from the USA aren't unusual either.