Yeah, I dont get this at all. I dont know when the song was written but the Sam & Dave version was released in 1968 or so.
So the words are copywrited when the song was written for 27 years I think, and then you can renew the copywrite for another 27 years. After that it should be free to use, open to the public for anyone. Maybe my memory is wrong though. After all these years still claiming ownership?