if you had the ear you could get the 'accent' of the man transmitting and hence twig to his identity
In a past life I was a signaller in the Rhodesian Army and Fantome is right. Accomplished morse signallers could be recognised by their 'hand' and if you worked with one, say, at Battalion level his rhythm would be such that you could write down words without assessing each letter.
I had difficulty in reading Pundits because they were too slow, the same with Consol and NDB.