This is a proprietary channel designation that is specific to Nady. They offer two VHF frequency ranges: 170-172MHz and 174-216MHz so it's a safe bet to assume that B/D represents 170-172 and P/R is 174-216MHz. It doesn't really matter which one you choose - just go with whatever is in stock. Keep in mind that VHF is good for wireless systems that aren't going to travel - such as in an HOW or auditorium. Your best bet is to call Nady customer service for clarification since they're not very forthcoming on their website.
