A commercial master printer is someone who can print other peoples negatives to match their (the photographers) own styles. It's a case of not necessarily printing someone else's negatives the way you'd think best for your own work but as they feel would be best.
But a master printer can also be someone who consistenly produces high wuality iomages from their own images over a long period of time, their feel may change but their style and flair is still there. John Blakemore is one of the true masters, but I'd guess Minor White would be similar, on the othef hand Paul Caponigro another renowned printer produced some sub stndard work shot in the UK in Megaliths
Ansel Adams was not a master printer, or at least not until quite late in his life. Early prints are all ovrer the place as an exhibition of images belonging to his daughter showed quite clearly when it toured the UK 3 or 4 years ago.