A C
"lyrics are seldom improvised...."
May be true nowadays, but certainly wasn't once. That's why we have upward of 200 versions of Barbara Allen.
Ballad scolar David Buchan suggested that there were no set texts, rather plots and commonplaces, and the singers recomposed them each time they sang them.
Point taken re Waterson's Dave, thanks - not my area of knowledge.
Jim Carroll