What do you know of the history of the truck? That looks to me like the tag that would have been on the driver side kick panel from an early one. Have you looked for the VIN on the frame (passenger side, above the starter, kind of below the passenger floor/firewall)?
If your glove box and doorjamb match, maybe that's the tag from a swapped frame? Does the VIN on your body plates match the one in the picture? If not, I would think it's the VIN of your frame, unless you know otherwise.
That said, there are guys on here that known this stuff way better than me. Someone will chime in with better info.