A,B,C stamps in passports of overstayers

You blokes on here seem to know a fair bit about all the legalities and visa issues in Taiwan,So I have a question for ya’s…
I am wanting to know what do the letters A,B or C represent or mean that are stamped in your passport as you leave Taiwan after overstaying?
Do they represent different time lenghths of the ban that has been imposed?

Well it looks like the question has them stumped? Any suggestions how to find out?