I know that they are very picky for cameras and lenses. Paranoid about "gray imports", they want to protect their huge profit margin on US sales. They check serial numbers to ensure it is a series that was sold in the US. They want you to register your purchase, but will not accept that online registration for warranty purposes, they want a receipt.
Even worse, I bought a lens as a Christmas present, it was on sale at a significant discount a few months before, so I bought it then.
Upon opening it at Christmas, discovered that the warranty required both online registration and the receipt. However, the online registration had to be made within 60 days of the date of purchase. By then, it was too late, of course. You could always lie to get the online registration accepted, but then the date would not match the receipt.
Nikon US management are assholes.