It is interesting that you can set the counter to 24 after the first 12. Actually that is not the way you are supposed to do it. You set the counter to 24 to start. At the end of 12 the camera stops advancing and you have to push the shutter button once, then advance the film again and it goes back to 1. That way you don't lose track. Also it leaves a larger space on the roll between the 12th and 13th frame when it is all done and processed.
You only need to remember to set it to 24 to start a new roll. A problem that occurs is if the switch is set sort of half way when you put a new roll in, the sensor won't sense the film and it will wind through a whole roll without stopping.