Correcting a muddy sentence- The Library was a repository; the Lomaxes probably retained all copyrights except for ....

Malcolm Douglas raises valid points. Some further notes, based on their editions of "Cowboy Songs":
The music for the 1910 edition of "Cowboy Songs" was prepared by Professor Henry Leberman of the Texas State Institute for the Blind. This contribution was not acknowledged until the revised edition of 1938.
For the 1938 edition, the music was revised "and/or corrected" and "not a few of the songs were taken from manuscripts furnished by both professional and amateur singers..." These contributions were not acknowledged in the book, except for a few which could not be overlooked such as "The Santa Fe Trail."
For this song, the Lomaxes printed words and music by Sherwin and Klickmann, copyrighted 1934 by Robbins Music Corp. ("all rights reserved including those of public performance for profit"). This song was written by James Grafton Rogers and copyrighted in sheet music issued in 1911. Another copyrighted version was "'Longside the Santa Fe Trail." This song and others have been saved from litigation only because "there warn't no scratch in it."

The Lomaxes admit making changes, "justified by the necessity of making them singable,..." (1938 Preface). These changes certainly could be interpreted as copyrightable arrangements.

Spiritual and Gospel songs- some copyrights are shared with the performers through the publishers.