"If it were to have a subtitle more acceptable to those who claim ownership of the term 'Folk Song' what should it be?"
Nobody "claims ownership over the term folk song" - well over a century's documentation and research has made that totally unnecessary

In my opinion the book would have been far better named 'A History of Popular Song'
When I was told that over 90% of our folk-songs originated as commercial commodities to be sold, 'no different than today's pop songs' that was the title that was suggested to me.
Using that description would have prevented these disputes and enabled us to judge the work on its own merits

I believe the folk Song revival lost its way because the term 'folk song' lost its meaning - I hope scholarship doesn't go the same way

"Titles don't matter if you have a clue."
We are a dying breed and desperately need new blood - most incomers don't have a clue
The present Irish Traditional music boom was launched on a carefully constructed foundation based on past work
Incomers can do and are doing what they wish with the contents of that foundation, but they will always have a reference point to return to
I never thought I'd live to see that point reached
Jim Carroll