In my most recent, and former, association, Black Belts (regardless of rank) were addressed as Mr, Mrs, Miss, etc. I prefer to address them by their martial arts title (Cho Gyo Nim, Sam Bum Nim, Bu Kwan Jang Nim, etc) because I was taught that we address our elders as Mr, Mrs, etc, and it has no bearing on their position in society (i.e. dojo). We are slowly transitioning...old habits are hard to break!