A good place to start is to compare them with Beaumont and Fletcher's play "The Knight of the Burning Pestle." (Actually thought to be entirely by Beaumont.) The character Old Merrythought sings many of the songs found in Ravenscroft's volumes. (Of which there were three -- note that Deuteromelia is the second delicacy!) It makes sense to assume that Ravenscroft, in those cases, was arranging existing songs.

Other than those, there is no reason to think any of them folk songs prior to Ravenscroft's publications. Probably, though, he was often setting existing texts.