Jim,
I can show you examples of communal composition but they're relatively few and certainly not ballads.

How many songs of the general corpus contain 'insider knowledge' that couldn't be obtained from a great variety of easily accessible sources? Newspaper reports spring to mind, keeping your ear to the ground in the pub when Jack Tar's onshore etc, battle reports. Perhaps you can suggest some well-known examples of songs with insider knowledge from the general corpus of English traditional song.

Hacks certainly adapted existing material, but more often than not the material they were adapting takes us back to another broadside.

Sharp was discredited with this stuff a long time ago.

Jim, you'd better get out there and start reconverting all the people who are happy to accept my hypothesis.