I apologise for double posting like this in a bid to bump, but I really need to ask a question that's been eating at me for a while.
I've found that I can make infinite merchant republic/theocracy vassals by granting Duke-level titles to burghers or priests while owning all the counties in the duchy. They don't try to take a county for themselves, they just become Duke (or Rabban or Archbishop and so on). I then give the counties away to courtiers and transfer the vassals over to the Dukes. Through this method I can create as many Merchant Republics/Theocracies as I like without going over the county limit. It tells me I have 6 counties in vassal theocracies but my Archbishops have no counties to their name, just vassals and a few temples/cities. It still doesn't say I am over the limit (which is listed as 1), even though I clearly am, unless Duchies are being half-considered to be counties or something.
It may be of note that in the duchies I was creating, I only owned one of the counties in each. All the rest of the counties belonged to other counts. When I made the Archbishop/Rabban, maybe he didn't try to take my county because it was the last one in the realm and my power/authority supersedes his.
Is this a massive exploit that I should stop doing right now? My head is exploding.