I think you miss the point Mr/Ms Gander
Where did Harry Cox get his songs from? Or did he write them...
Don't get me wrong. I love hearing singers and musicians recorded in the early 20th century, and have had the pleasure of meeting many of them. But, time moves on.
Of course it's wonderful that all these archivists, collectors, whoever are digging out old manuscripts/broadsides etc.
From Child onwards. Not forgetting Doc Rowes massive body of work re the English tradition Great stuff.

You say "The term source singer has an accepted meaning"
Accepted by who, exactly?

Well, unless defined accurately. I'll find my songs/tunes where and whence I can. If thats all right with you.

All very useful as source material.