If you look at the sources of the songs collected by Sharp and his colleagues, you will see that they covered a relatively small area of the British Isles and represent a tiny area of Britain.
They were virtually head-hunting songs they believed were rapidly disappearing -
The urban areas were barely covered.
They always claimed that they were collecting from a rapidly dying tradition, which was probably true in most cases.
Taking Britain as a whole; their collection is in fact quite small.
Take a County the size of Norfolk, probably one of the richest areas of Britain, and you will find that the number of informants represent a pinprick of the population in general.
Some forty years later, when the BBC carried out their mopping up campaign, the number of singers had reduced considerably and by then, they were recording from singers who were largely remembering a tradition rather than reflecting living ones.
Walter Pardon was a remarkable singer with a sizable repertoire, but he could only remember songs from his family tradition, which happened at Harvest Suppers - the few songs he learned from outside the family came from basically one man, and they were largely of music hall origin.
He could not remember hearing another local singer.
Jim Carroll