In understanding how someone would 'claim' they wrote a song - you can't apply today's criteria to that time - especially the early 30s. The idea of copyright on a recording rather than on sheet music was still new. In general, musicians were being taken to the cleaners rather than the other way around. It was NOT a case of plagiarism that you might encounter today. Alton Delmore was a serious musician and artist. I would assume that he arranged the music that drew on traditional sources. That he was paid $1,500 for Beautiful Brown Eyes (he could not afford to litigate further) indicates that there was absolute truth in his claim to being a writer of it. I once asked Wade Mainer about a song he recorded - did you write it, I asked. He said - it was the theme song for my radio show and I changed it enough arranged it enough that you can say I wrote it. And he is given credit for having written it.