Board Thread:Plants vs. Zombies/@comment-25157225-20150914051732/@comment-1764483-20151128155626

They're mentioned at Hybrid mini-games.

To make it more blunt, 0 is Adventure Mode, 1-15 is Survival, 16-35 are mini-games, 36-50 are limbo page items, 51-60 is Vasebreaker, 61-70 is I, Zombie, 71 and 72 is more Limbo Page stuff, and 73 and both is nothing (i.e. a game crash if you access those levels).