A very interesting thread and reminds me of when we had steam, that AFAIK, it was not necessary for a qualified driver to train for specific steam traction, but that was due to the fact that he would have spent perhaps decades as a fireman and would have worked all the traction by the time he was raised to driver. That's different now with single manning but with company-specialised traction (typically) he /she (note the she) would probably now have to learn new traction on switching companies. Is there a certificate system to shew for which traction one is qualified? Can one take that from one, say, FOC, to another, e.g. class 66?
This is apart from route learning and signalling of course.