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I suspect that when online polls like this are compiled, they MEAN only hitparade pop music....I doubt that they even count how many recordings of "Barbry Allen" there are..or of "The Two Sisters" (LOTS!).....and Mudcat is, supposedly, concerned with folk-related stuff.

It may be of passing interest to know how many Beatles songs have been covered, but I'd venture that some 'folk' items would be much higher in that list than many of the ones that ARE listed.