Certain games are JAMMA but with extra connectors/connections for different things that aren't used by the JAMMA standard. For instance, if you plug a Street Fighter 2 PCB into a standard JAMMA cabinet, you won't be able to kick, since there will be no buttons for kicking. Smash TV is another JAMMA+ game, instead of using buttons to fire, it uses another joystick. If you plug a Smash TV PCB into a JAMMA cabinet, you can play, but you'd only be able to fire in three directions, and you could possibly crash the game by telling it to fire in opposite directions at the same time.