Jim, Tom,
I think we're really singing from the same ballad sheet here. I'd say all 3 of us were in 90% agreement at least.
Jim, I too have collected quite different versions of songs of the older type from 3 people living a couple of doors from each other.

Tom, I too am interested in David Buchan/Albert Lord's theory on ballad improvisation and am becoming convinced by it, although I think both methods were employed simultaneously, 1) journalistic ballads being composed on historical events like most of the Scottish historical ballads 2) Ballad remaking each perfomance based on solid knowledge of the story and a repertoire of stock verses/phrases. I'm not so sure about the balanced construction theory but Buchan presents a strong case.

Jim,
I didn't think there was anyone still alive who subdscribed to the communal composition theory. There are obvious exceptions Tom has mentioned but ballads of the Child variety and broadside ballads certainly don't come into this.

Regarding the second method I have started experimenting with this. I now sing 2 Child ballads, Cruel Mother and Two sisters, without learning a set text, just based on a set tune and refrains and my knowledge of the basic story, so each time I sing them is a different performance.