IIRC, how it determines what map loads when the (game_won) function is run is hardcoded. If you have an a10.map, a20.map, and a30.map, it will skip right over a20.map and load a30.map.

That also means that it can't track what levels you've unlocked in the main menu if you were to add more maps and then just change them with (map_name) instead of (game_won).