Not all the songs, Joe! Just those that were identified as spirituals. There is still a five-foot shelf of material left in the 1939 trip, on a large variety of subjects.
The site is well worth investigating because loads of ideas are there for the singer, performer, or anyone just plain interested in folk songs and how people change them around. A real portmanteau!
The materials are also a record of a culture that pretty well disappeared just a decade later, with WW II the disruptive agent.