If at all possible, please give as much information as you can about the sources of songs, especially if you know of printed sources that pre-date the Carter Family.
I handle licensing for a musician or two,* and it always bugs me when we have to pay Carter Family royalties when I have a strong feeling the song pre-dates the Carters. Oasis is particularly fussy about making sure all songs on cd's they manufacture are properly licensed, so it helps to have solid proof that a song is in the public domain.

-Joe-

*this is not a money-making thing, but it's fun. The only payment I get is a free CD and an occasional kiss on the cheek.