Shimrod and Jack Campin have it dead right. All collectors (the ones I have met anyway) set out with the idea that they will record as much as time and circumstances allow them to, including information.
However, faced with singers like Tom Lenihan (200 songs) Mary Delaney (about the same) and Walter Pardon (around 150) we found ourselves constantly having to prioritise.
We set out as 'folk song collectors', having some idea what we meant by the term, and in the limited time we had available to us, they were our priority. If we (and the singers) had the time, we always recorded everything the singer was prepared to give us, and then get he or she to talk about their repertoire. I suggest you listen to what Walter Pardon had to say about his repertoire, some of which can be found in an article I wrote for Musical Traditions 'Enthusiasms' section, entitled 'By Any Other-Name'. Travelling woman Mary Delaney refused to sing her non-folk songs (mainly C&W), telling us that these were not what we were looking for and "the new songs have the old ones ruined" - she only sang them in the pub because "that's what the lads ask for".
Sharp, who started the ball rolling in England, based his 'Conclusions' on his extensive work in the South of England, Karpeles did so on her work with Sharp and her own in Newfoundland, Greig's massive collection came from is field work in Aberdeenshire..... how far do I have to go?
If they - or we with our 36 years recording farmworkers, fishermen, Irish and Scots Travellers, Irish construction workers in London.... all got it wrong, it really is time that somebody told us where we did so - and maybe compare what we did/do with their own efforts rather than resorting to the usual method (much in evidence here) of argument by innuendo.
It has always been my experience that people who ask such prattish questions as "Does folk exist" invariably do so from the comfort of their armchair, or a folk club, and usually have their own particular agenda, usually setting out to prove it doesn't, as likely as not in order to be able to justify their hangining their own particular preferences on the 'folk' peg.
Incidentally, to whoever suggested that it would be helpful to know what the person coined the term 'folk' had in mind, antiquarian William Thoms (1803-1885)first used the term 'folklore' in 1846. There is an entry on him the Funk and Wagnall Dictionary of Folklore, Mythology and Legend, and a gread deal of information on his work and ideas in Richard Dorson's 'The British Folkorist'.
Jim Carroll