I'm starting to think that there are more than 12 songs in this game. Maybe 12 selectable background songs but there are surely several other mode driven or boss fight ones. I've been looking a lot on gameplay from the mobile game and how that world and bosses are presented. Stern talks about going on an epic quest with Eddie as the protagonist fighting minions (exactly as the mobile game) and every world features a different design and integration, of which all are presented on the playfield.
Stern haven't spilled everything yet. I hope.