Sorry, going to have to disagree diametrically with both of you. One of the characteristics of folk, as against art, music is its protean nature. Nothing is fixed or given. You could describe it as evolutionary by its very nature- including mutation and natural selection.

Each singer takes any given song, and applies their own meaning. Young Rambleaway can be sung as a sexist song of uncaring male privilege, or as a desperate cry for help from a man who wants, but can't achieve, meaningful relationships. Dirty Old Town has been applied by singers to the townscape they knew (or imagined), and that's how it should be. McColl saw himself as a folk singer, and wrote a song, not just a gazetteer of Salford in the 1930s (or whenever), but about love in an archetypical industrial town. That's why it's so popular, and not just among committed folkies.

As an aside, my Dad thought Dirty Old Town was specifically written for him (he was from Hanson St). But then he also thought he was the subject of Robert Roberts' works about Salford, The Classic Slum and A Ragged Schooling. Even though he was a dozen years younger than Roberts.