Chris,
Charles Erskine was born 1822 in Roxbury, Mass. His death was reported in the Boston Globe on 21 December 1900. The ship CHARLES CAROLL (Erskine spelled it "Carol") was a cotton-carrying packet ship that certainly plied the Boston - New Orleans route at that time. There are even two photos of Erskine in his book, with attribution; it would be quite a ruse to make that up with such detail.

Yes, it's quite possible that Erskine made use of Nordhoff to "refresh" his memory of the songs he allegedly heard 50 years earlier. Lyrics are very similar. I see no reason, however, to doubt he had first-hand contact with cotton-screwing in New Orleans. Whether he actually heard those songs or pretended to, we'll never know. Yet one could play Devil's advocate and ask why Erskine would not have copied Nordhoff verbatim. Why mix things around? It looks to me more like using Nordhoff to fill in a vague memory, rather than making up something that never happened.

Erskine, he says, had no formal schooling, so there is something perhaps fishy going on, like he got some help.