This is how i understand it operationally, but i may be completely misinterprating the charts (AERAD).
B-Rnav you require atleast one point that you can fix your position using raw data before descending below MSA. P-Rnav, you don't need any points for dme/dme or vor/dme assuming regular failure rates.
The only place that really confuses me is PRG. No points to fix yourself below MSA, however you can continue B-Rnav if you're not P-Rnav certified you what now??