I think the term "source singer" makes a useful distinction, but when you look at it too closely it starts to break down.

For me, an important part of the distinction is not just whether the singer learned their songs orally, but the context they learned them in. A source singer should be part of a continuous community (although this may now be moribund) . They should probably not be too self-conscious about their songs - they may distinguish between folk songs and other songs but they will all just be part of their repertoire. A revival singer, on the other hand, will probably have made a conscious decision to create a repertoire based on folk songs.

I've learned most of my material by ear, from both "revival" and "source" musicians and directly as well as from recordings. But I would never consider myself anything other than a "revival" singer/musician, because I did not learn these within such a community. I came across folk music by chance, decided I liked it, and chose to pursue it.

But within the revival we may by now have created such a community. We used to affectionately refer to source singers as "old boys", but soem of them were not much older than I am now. If a collector were to walk by chance into my local pub on Friday night he would find a community of musicians of all ages and backgrounds playing and singing. This has been going on for at least 30 years and probably longer. Are we an exciting new undiscovered source, or just a bunch of folkies at a session?