Thanks for the detailed research.
Minor additions. "Black Them Boots" is in Randolph's Vol. III (no. 550). "Scraping Up Sand In The Bottom Of The Sea" is on Mike & Peggy Seeger: American Folk Songs for Children [with sound clip] (Rounder), CD (formerly LP) version of Crawford Seeger's book. Info on "Patting Juba" in the antebellum days is in Dena J. Epstein, Sinful Tunes and Spirituals (University of Illinois, 1977, pp. 141-144).

~Masato