There has never been any need to add 50 feet to a precison approach because the 50 feet is already built into the usual OCH of 150 feet which would give a Cat 1 DH of 200 feet if the OCH is 150 ft as it is in most UK airfields
A NPA has never had the 50 feet built in as it was originally a dive and drive approach. When the airlines changed to continuous descent approaches after a few dive and 'loose control approaches' the 50 feet was required to be added on, that is what we were told by the CAA ops inspectorate at the time.
Somebody mentioned altimeters-the 50 feet has nothing to do with altimeters its purely to stop infringement of the approach OCH during a GA