JAMMA+ simply means they used additional connections for the game, than the JAMMA standard allowed for. JAMMA is the card edge pinout, any extra connectors for more than 3 buttons is probably on a separate harness. Trackballs are usually also on a separate harness.
FYI, Almost all games that are JAMMA only use a subset of the pins as needed by the game, so even if a cabinet has a JAMMA game in it, it doesn't mean all the signals are hooked up to controls. A good example of this is the -5VDC. Most JAMMA games only need +5 and +12, so they don't bother hooking up the -5VDC lines to the power supply.
HTH! Best,
- Mike -