>> So presumably we're not talking about adherence to the historical facts, but adherence to the intentions of the original writer of the folksong. <<

I don't think your post was directed towards me, WLD, but let me explain a bit more, using the previous example of the schoolkids and the mill songs.

I could sing them a song I'd written, after proper historical research, that gave them an accurate and quite possibly harrowing account of - say - child labour in cotton mills.

Or, I could sing an old song, telling them: "This is what people at the time were singing about the cotton mills."

Since singing old songs is what I do most of the time, the latter would be the more likely scenario (and would fit with the ideas I grew up with about the stories old songs can tell us). In which case, in order to be able to look myself in the eye, I would have to be confident that the 'old song' was exactly what I said it was, and not a product of the folk revival post 1950. If it were the latter, no matter how historically accurate the picture it painted, I wouldn't be making an honest presentation.

I'm not suggesting here that Bert Lloyd systematically faked songs about conditions in the mills, just giving you an example of why this kind of thing matters to me.