Pre-1978 copyrights are not online.

But the U.S. Library of Congress Copyright Office will check the copyright status for you "for a fee." (Don't know how much.) You can find out more by calling 202-707-6850. Be sure to mention all possible variant titles!

If you have access to a large library, they might have the multivolume Library of Congress Catalog of Copyright Entries, which goes back more than a century. A librarian might be willing to look up the copyright for free.

Good luck!