Yes - newly written songs were included in the traditional repertoire - all songs started somewhere, but it was the process that made them folk songs, not their being sung
The logic of your argument is that every song a traditional singer sings must be folk necause he/she sings it, so if Sam Larner sang Nessun Dorma, it would automatically be a folk song

The new songs can never be traditional folk songs ~ they are contemporary folk songs ~ Jim you cannot pinch or copyright the word Folk or folk

Ray Padgett