folk songs evolve and are not made

No. Folk songs are first MADE and then they evolve, or maybe they don't. Maybe even in their natural habitat they remain unchanged - like George Bruce Thompson's McGinty's Meal an' Ale - which he wrote shortly before it was quickly snapped up by singers (Davie Stewart) and academics (Grieg & Duncan) alike. It remains unchanged to this day - but a highly evolved class of a Traditional Song even so. Then there's the songs of Tommy Armstrong, and other amazing things like The Keilder Hunt, The Shepherd's Song and Til the Kye Comes Hame - each sung by one of the finest Traditional Singers (Willie Scott), each with a known author (one may even have been written by him), each of them unchanged, and yet each totally and undoubtedly a bona fide Traditional Folk Song. I'm sure they might even have Roud numbers burned into their hides by now.