

Nothing is stored to tie carts to hardware or accounts.
Do you remember the discontinued gold points program? For any brand new physical cartridge you could claim equivalent to 1% the game’s price. Obviously the points could only be claimed once, by a single account. This seems to point pretty strongly to carts being uniquely identifiable and to Nintendo’s ability of keeping track of usage.
I recalled differently so I looked it up. Here’s a video of a random person claiming their points. No code-in-box, just the console phoning Nintendo with cartridge inserted.