There used to be a first digit indicating the marketing region but when really popular cameras started running out of numbers they dropped that as an iron clad policy. Then the Z cameras came out and there is no sure indication with those bodies. So is it grey market? Asking Nikon is the only sure way but even they have been reluctant to say recently. IF your registration of the product after purchase went through ok on the web site, it is accepted as a camera covered by that region's warranty.
The person who replied that GPS means US is clearly uninformed and should not be answering since they are probably the janitor and not a customer service dept employee. The only restrictions on GPS are usually related to accuracy, banning highly accurate resolution as a security risk in the US. Other sat nav systems do not cripple their GPS accuracy.
GPS is allowed almost everywhere. What IS different in some countries are the WiFi frequency differences but almost all hardware can cover them all.
Regardless of documents in the box, your warranty registration on the Nikon web site establishes and extends the warranty so be sure to go to their site and register any new purchase.