Re: Standard German and Dialects?
"I think I read somewhere that elements of "personalisation" in the source messages did come into it. Each operator had their own keying style, so the interceptors knew who it came from, and certain operators would have little quirks in their message content."
Yes, this was a known "feature" of telegraph operators almost from the invention of the telegraph. There many stories around of telegraph operators knowing who was "calling" from way the Morse was tapped out. No doubt any Ham operators still using Morse have the same experience today with their regular contacts.