I tried a while ago to get to the bottom of the "100%" but it led me to another thread and got too confusing so I gave up. I believe the only place it has appeared in this thread is in posts from Jim attributing it to Steve G. I don't think anybody has ever really claimed 100% print origin even for the classic corpus, let alone for the totality of folk song. As for that figure being "extended to folk tales and tunes"; I missed that, but clearly such a claim would be nonsense.

The Carroll doth protest too much, methinks.

Picking up the separate matter of modes, raised by Pseudonymous: Sharp wanted the tunes to be ancient, so seized on and gave prominence to ones that seemed to correspond to the old church modes, but I reckon Grainger's interpretation was the right one.

Another instance of variability is in Cecilia Costello's alternative cadences for The Grey Cock, implying major or minor.