I do some times wonder about even official names.
Train driver UK, Engineer US
Fireman on a train, Stoker on a boat.
Many names origin in Latin as Plumber is a worker of Lead, and when I was a lad they would also do the flashing on the roof.
Pipe fitters I knew worked with 36 inch heavy wall steel pipes, and there was no question very skilled, using interferometry to measure etc.
So what is the name for some one who works with copper or plastic pipe, can't call them a pipe fitter, that trade already exists, can't call them a plumber even the solder is lead free, I suppose it is not really a trade, but just part of a trade, so a heating and ventilating engineer would learn how to work with copper and plastic pipes as part of their trade. However is heating and ventilating a trade or a profession? As with electrician or electrical engineer, up to and including level 3 is an electrician a trade, above level 3 an electrical engineer a profession. Other than US engine driver engineer means degree standard.
So today is Plumber a nick name, few still work with lead, organ builders are called organ builders not plumbers even if they are one of the few trades who still work with lead.