It's 9 ball with 3 more balls. Rack for ten ball and add two balls on the back with a space open in between. With a perfect rack you should make A LOT of balls on the break, since the two corner balls are dead into the bottom corners.
only time i have heard of 12 ball is when you are beating the 10ball ghost and need to add more balls. Alex Pagulayan was beating the 12ballghost at the derby one year