Dusting off this nugget for use in a larger game, and I just re-read your question in a new light: As written, you can't roll over 12.
Each die is its own result/beat/effect, and the d12 is the largest die in the bunch. So the game is designed with only 1-12 as options. If you roll 4 dice, you would get 4 different beats to role-play, but each one would be from the 1-12 list.
Bringing in a d20 would then expand 13-20, as we chatted about below. But you'd have to bring in the d20 to get a number higher than 12.
Apologies if I went too design-hypothetical in my original response when your question was more mechanical/clarification.