Hi ffolke,
   It's nice to see young people take an interest in traditional music.
It has many definitions and subjective borders, and stuff that appeals to many different tastes. I would suggest that you have made a key start in locating Mudcat. Spend some time reading through the DT lyrics and the forun archives. There is much there to be learned, but you will also find garbage so don't believe everything.
You Are My Sunshine, by the way, is not public domain as it's author, Jimmie Davis, died in recent years.