You had store variants, not for resale cartridges, games meant for the military, and so on. The NES arrived before systems like the Genesis and SNES, so the rarest games can be very difficult to find.

1990 Nintendo World Championships: Gold Edition (NES): $15,000-$21,000 There are ... "Birthday Mania" is one of the rarest games of all time. "Birthday Mania" allows players to play mini games ...