"I think it is both mediation and comment on the mediation of traditional sources by singers."
Thar depends entirely on whether peoples estimation of folk song is based on personal taste - it shouldn't be and, in my experience seldom is
If there are no specific examples produced the suggestion remains no more than a "what if"
Folk song collectors decide to collect from people who know folk songs - what else should we do ?
We'v been through the difference between folk song collectors, musicologists and social historians
I think Howard is sport on - we used to talk about collecting from 'traditional singers' - then it was argued that the revival could lay claim to having its own traditions
'Source singers' is ok with me, but the way things are deteriorating, I expect to have to fight to hang onto that particular musical chair in the not-to-distant future - which is why I'm quite happy to cling onto a century's research and usage
Repetition and continuity is only a small part of what makes up traditional song

"'practised' source singers who handle a 'break' in their vocal range"
Most of our source singers were old and way passed their prime - we would have lost a hell of a lot of songs if collectors in any way 'prioritised'
An extremely rare Irish and treasured version of 'Well sold the Cow' was recorded from a Clare singer dying of throat cancer - he had a great deal of trouble producing tune, never mind handling a break in his vocal range'
I've never been in the position where I've had to 'leave out' any singer, no matter what they sing - it tends to leave you with a bit of a reputation
I'll tell you the story of recording light opera from the 'bare-fist fighter' Donegal Traveller sometime
Jim