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