Hi Wes, Not unusual for that southeast PA area. I think what you might be seeing as unusual is the interior shape of the box cavity. I would guess that that as originally intended the interior shape would have been much like Taylor's Beck style box, but w/o the ledge to set the release spring. The maker had to remove material at the top rear to allow the spring to flex upward to release the box. The amount of wood taken out at the back whether by mistake or design is a little on the crude side. Of course we do know when the extra wood became missing or who may have messed with it.
Ron