I know that many of these songs have been passed down from singer to singer and are still being sung.I also know that besides getting songs from other singers, people like Martin Carthy got many of the songs they did from the Childs ballads. Just take a look at his new box set "The Carthy Chronicles", there is a whole cd of just songs from the Childs ballads. Plus he told me personally that he got a lot of the songs he sang from them.
In fact many of them I had never heard anyone do "on recordings" before he did them.
Terry