Unless there has been a major sea change, the +50 is a requirement if the aircraft does not have a published PEC in the flight manual.
Whilst PEC may indeed apply, I'm not sure that this is what is being discussed here. If you are applying a PEC of, say, 50 ft, what was a DA of 400 ft now becomes 450 ft. In any event, PEC does not apply to NPAs with a published MDA, at least in the UK.
Pete - you said that you are content for a candidate to go below DA, is that the official line for IR?
Yes, provided the MAP has been initiated within the tolerances previously stated.