I have one of those questionable circuits too. There are 2 20a circuits in my master bathroom. One hits my wife's side (3 times) and the fan ... OK
The other hits my counter receptacle and the 1/4hp whole house fan. The inspector didn't figure it out and I didn't tell him. I am not sure I have plugged anything in there in 10 years. My wife has all 6 of hers full.
I am getting ready to do the guest bath and I have the same question as Kjay. Do I have to abandon the existing 15a if I add a 20? (I'm not going to but I am curious)
