Open them only to the Table of Contents, Itemize the songs there in. Note the publisher and publication date. Fire the list off to the Library of Congress and see if they already have these works and songs avaiable as copies. What do you care which publishing the songs come from as long as they are the same songs from a recent or more recent edition of the book in question.
This may help to keep your books intact. I'd contact a paper conservator or an expert in Ephemera conservation. This is different from restoration.