Jude,
Most of the radio officers in UK and elsewhere went to maritime college for radio officers. The auditor was their Morse instructor during the two years of training, then they had to pass the post office examination (we had FCC) and since these were commercial licenses they were quite strict about their evaluations.
These days, there are software programs like FISTCHECK. That can do the work.
I had a DGM SRT-2000 keyboard which could send and receive and when I was sending on my semiautomatic Vibroplex key, I would monitor it to improve my sending, at first even with practiced use, occasionally "C" would be decoded as "NN" I worked until the DGM SRT-2000 keyboard could copy me perfectly!
73
DR
N1EA