The Amos referred to is Amos Easton. He released it in 1934. He used a few aliases.

https://secondhandsongs.com/artist/34351

I think this will help explain the whole who's who and got what from whom. Read p. 295 from the following link.

https://books.google.ca/books?id=-w-uGwm_LhcC&pg=PA295&dq=Sonny+Boy+Williamson,+Sail+On,+little+girl,+sail+on&hl=en&sa=X&ved=0ah