A problem you seem to be having here is more clear cut this side of the pond. Versions of songs recorded by shall we say professional performers like Lloyd and MacColl in the revival(say 1945 to present day) would not normally even be contemplated as valid study texts for traditional songs unless one was studying what the revivalists did with the songs. I have noticed before posters on the Ballad List, for instance, mentioning songs recorded by the likes of Lloyd and MacColl as though they were from traditional singers.

I understand that many traditional source singers on your side of the pond also became professional singers and even collectors in their own right, and this then presents problems. Although there are a few performers who would come into this category this side, they are few and far between and we are more often aware of the different sources of the songs in their repertoires.

I sometimes feel we are using words like 'dishonest' a little too harshly with performers appropriating material and then not quoting or revealing their sources. 40 years ago just about everyone did this. If a song was in the public domain, if you were a performer as opposed to a researcher/scholar, the source would have been of little interest, and might have created copyright problems as you say.

Even some scholars at the time were a little negligent with the truth. I am working on new editions of the Marrow Bones series of books and it is obvious that the original editor was occasionally taking material quietly from other collections than those being flagged up, to make up his collated versions. Today this wouldn't be a problem but in the 70s the other collections were in private hands and the owners might have objected if he had been more open.
Even had they been willing it would have taken up valuable time getting necessary permissions, for the sake of just a few verses from a range of collections.