IS you're right they are a very pure form of folk,surely. nobody knows who wrote them, they are recognised as common property, and orally transmitted. Those should be good criteria. Ed is probably right, they do miss out by passing quickly I suppose. I've forgotten loads, we used to know parodies of ads but they seem to have flown from my old brain. I can remember one playground pop song parody:
The Yellow Rose of Texas
The man from Laramie
They went to Davy Crockett's
To have a cup of tea
The tea was so delicious
They had another cup
And left poor Davy Crockett
To do the washing up