On patented items, the thing to remember is the patent may just refer to one part of the object (in some cases, items were marked patented that never were) and not the object as a whole. This patent date refers to his original patent improvement for a knife-sharpener that was granted on May 3, 1870. He added the glass cutter and patented it later. being that the wood handle is marked and not the metal (have you looked real close for any markings on the metal?), I would guess he used old handle stock from his earlier patent to assemble this one. A common occurrence. Thrifty is as thrifty does.
I found the same image you posted but there was no glass cutter which is quite obvious on your tool, so I put "stokes knife sharpener" into the search and the later patent that included the glass cutter appeared. As I was about to post on the forum, you also posted, so I had to adjust mine a little.
