The only way to tell for sure would be to dump the binary and anaylze the code. If this is NTSC, you probably have the only known copy in existence.

Perhaps there was a limited pressing ( you had said it is NIB) that never saw the light of day that is still sitting in a warehouse somewhere.

Did the shrinkwrap look like it was on since the cart was manufactured, or was it loose and flimsy? It may have been reshrinked with someone putting the N on at a later date.