There is a bit of information missing in all of these places(as far as I can see), and that an explanation of what the nature of a copyright is, and how the ownership and control are divided between author and publisher--

Basically, the Author or authors who created the work split the royalties with the publisher, who controls the publication or use of the work.

People are often perplexed as to how Michael Jackson could have purchased the rights to the songs that Paul McCartney and John Lennon wrote, and, simply, it is because he bought the publishing rights--which belonged to Northern Songs, while McCartney and Lennon's heirs retained the author's rights.

Of course, as in all things, things get slightly more complicated, but this is not a legal opinion, and hopefully, you will not attempt to use my explanation as legal advice of any sort--