One of Susannah and Johns children was my gggrandfather. John and Susannah were married as Thornberry as well as their siblings, John Starnes and Elizabeth Thornberry when they married each other. My gggrandfather, Ira, was also married as Thornberry, but his brother, Isaac, was married as Thornsberry, John and Elizabeth changed their names when they going to marry out of the quaker faith. So, I suppose that means either, or maybe neither, spelling can be considered correct. John and Susannah 9th child of 13 was named Nancy if that helps any.
James R. Thornberry