I have at least one songbook that does not appear to be indexed on the website. How useful are these indexes to people in general?

The one book I did not see indexed is Maritime Folk Songs by Helen Creighton. ISBN:0-919948-85-5

A second book that I have not looked for at Mudcat is "The Ballad Repertoire of Anna Gordon, Mrs. Brown of Falkland. ISBN: 978-1-89797-632-6

This likely should be asked separately, but is it likely all the songs from these collections are already in the song database? Is there any systematic effort to put songs from collections into the data base? Is it "legal?" Is it even necessary or desired? (I am sure other song collections exist online.)