Just from the vinyl catacombs, not only folk, no birth months though:
Aaron Neville
Armando "Chick" Corea
Captain Beefheart (Don Van Vliet)
Charlie Watts (the only '41 vintage Rolling Stone or Beatle.)
Dan Hicks
David Crosby
David Clayton-Thomas (Thomsett)
Doug Sahm
Dr. John
Eric Burdon
George Clinton
Gheorghe Zamfir
Harry Nilsson
Jim Seals
King Tubby (Osbourne Ruddock)
K.T. Oslin
Lainie Kazan
Little Anthony (Anthony Gourdine)
"Long" John Baldry
"Mama" Cass Elliot,
Mike Love
Otis Redding
Paul Kantner
Ritchie Valens
Steve Cropper
Twyla Tharp
Wilson Pickett

Not sure what it really means. I got a pretty amazing list for every year I tried.