I have been trying to summarise what Harker says he is doing, the account he gives in the introduction of what the argument of the book will be. His concept of 'mediation' is important. I started by looking at that because he calls the people whose work he discusses 'mediators'. Two examples of mediators are Child and A L Lloyd. The former compiled a famous selection of ballads and the latter was, among other things, the writer of an influential book purporting to set out a history of 'folk song' in England, 'Folk Song in England' as well as an earlier shorter piece on the same topic.

Harker says that 'mediation' refers not just to the fact that people (the ones he discusses) passed on songs they had taken from other sources but also to the fact that what they passed on may have reflected their own 'assumptions, attitudes, likes and dislikes' in that these determined what they looked for and what they accepted and rejected. In addition, Harker points out that what he calls 'material' factors were involved, such as the fact that some people had the time and resources to engage in their mediating activities at all. He says that the class position of those doing the work and their ideologies will have been connected in complex ways. The latter is a classic Marxist point, I suppose.

The term and concept 'mediation' seems to have been useful: Dave Hillery makes use of it in his comparative thesis related to Jack Beechforth and three other singers. It is on page 24, 69, 95, 152, 157, 320. The thesis is here: https://theses.ncl.ac.uk/jspui/handle/10443/158

Hillery suggests that some singers themselves engaged in 'mediation' with Joseph Taylor offered as an example. He also suggests that collecting a song shorn of its customary context is another form of 'mediation'.

So it might be interesting to discuss whether this concept of mediation is valid and useful? Just a suggestion.