Cap'n,
We got to the tradition (proper) when it was very much in decline and many of the singers had not sung their songs for years, sometimes decades; in those circumstances there are bound to be changes, often brought on by memory lapses.
Ballad scholar David Buchan put forward the the fascinating idea that at the height of the ballad singing tradition there were no set texts to the ballads, just plots and commonplaces (milk-white steed, snowy white breast, silver pin etc) and a set form which allowed the singers to re-create the ballad every time they sang it. If that was the case, it is possibly this that James Hogg's mother was refering to when she accused Sir Walter Scott of killing off the ballads by writing them down.
It helps to remember that we are not 'traditional singers', just singers of traditional songs - we are not continuing the tradition, merely borrowing from it (thereby hangs an argument).
Jim Carroll
PS John Brune was the feller who nearly sabotaged the Radio Ballad 'The Travelling People' by pretending that songs he had written were genuine Travellers songs - thereby undermining the veracity of the programme. He is the reason that Sheila Stewart was never included in it.