The Fifes' book has caused some confusion in book lists and bibliographies; sometimes listed under Thorp, sometimes Fife and Fife.
The spine reads "Songs of the Cowboys," Thorp and Fife. The jacket cover reads "Songs of the Cowboys, The First Printed Collection of Cowboy Songs Collected at the Turn of the Century by N. Howard ("Jack") Thorp News Print Shop, Estancia, New Mexico, 1908." Separated below a line- "Variants, Commentary, Notes and Lexicon by Austin E. and Alta S. Fife. Music Editor Naunie Gardner."
The title page reads "Songs of the Cowboys" by N. Howard ("Jack") Thorp. Variants, Commentary,.... by Austin E. and Alta S. Fife. Clarkson N. Potter, Inc./Publisher New York, 1966.

The book includes a facsimile copy of Thorp's 1908 book, with songs composed by Thorp marked in MS by Thorp. These are "Little Joe, the Wrangler," "Chopo," "The Pecos River Queen," "Cowboys New Years Dance," and "Speckles."
Variants include songs not easily found elsewhere (examples in next paragraph), and the book is worth having for these alone.

Looking at just one of the songs, "Cow Boy's Lament," Commentary and Notes are extensive; pp. 148-190.
Variant texts known to the Fifes are listed, with significant variant verses quoted. Music for five variants is given. Texts of seldom heard variants are included, e. g., full text and music for "I Once Was a Carman in the Big Mountain Con," sung in the mines of Butte...about 1905 (Western Folklore Quarterly), texts of "Old Time Gambler's Song," Gordon 1720 from singing by Terrell McKay, "The Wild Lumberjack," and others, some untitled.
In other words, the book does include songs which have not been widely disseminated, but not from Thorp files.

Bibliography on "Cow Boy's Lament" covers some eight pages, and includes manuscript collections, recordings and discussions, dated from 1872? (Dodge City Journal) to time of publication.