Other than their book it appears they have no copyright registrations filed.
So? You don't need to register copyrights in order for something to be copyrighted, it just proves you're the owner, which could help if you need to take legal action.
True, but you do need to register your copyright if you want to be able to take legal action in U.S. courts. Just stating the copyright does not provide you with protection in the court system's eyes.
Other than their book it appears they have no copyright registrations filed.
So? You don't need to register copyrights in order for something to be copyrighted, it just proves you're the owner, which could help if you need to take legal action.