In his bio of Lomax, John Szwed writes:"Collectors copyrighting folksongs was not unusual at the time. Carl Sandburg, Zora Neale Hurston, Bela Bartok, Cecil Sharp,Percy Grainger, Ralph Vaughn Williams, and even Lawrence Gellert, the most politically leftist of all the collectors, all filed claims for copyright, though none of them shared earnings with the singers." Alan did share his earnings with the singers from whom he collected.
Neither Alan Lomax nor his father ever filed claims for copyright on individual songs. It was their book publisher Macmillan who did this -- by 1950 the copyright devolved back to Alan. It was a large music publisher, who looted their entire catalog during the 1950s, filing copyright on the songs using false names, such as "Paul Campbell" (among others) as author. Alan Lomax sued them, winning a partial settlement in which he was allowed a portion of the author's half of the earnings (contrary to his wishes) as collector and arranger. He would have preferred to have had a segment from the publishers' credit. Thus, Lomax is being excoriated today for winning a settlement in a lawsuit with a large corporation, which still owns the copyrights and is still raking in mechanical and other fees (50% of the royalties).