I am in complete accord with Brian. I learnt many songs from my grandparents, mother and uncles who had markedly different repertoires of traditional songs. However, I came to learn them after I had already become an active participant in the 'Folk Scene'. Indeed it was the 'Folk Scene' that inspired me to revive the family songs. For the vast majority of the people on the British 'Folk Scene'
for the last 50 years 'traditional singer' has always been used to refer to performers who came from a singing community other than the 'Folk Scene' albeit a farming community, fishing community etc.
However, more recently and increasingly I have heard the term 'source singer' used in the same way. Just as the term 'folk song' has evolved to encompass a wider meaning, it appears 'traditional singer' has confused some people (evidence above)and seems to be evolving a wider definition.
Like Brian, I will continue my practice of 40 years or so and continue to call 'source singers' 'traditional singers' and if that confuses anyone, I will expand on it quite happily.