My knife had the same etch. Scales were some kind of black plastic. There may have been 3 pins but I recall the center pin for certain--it was probably the first knife I disassembled and I had trouble removing it. My brother was a flag-waver on an aircraft carrier, don't recall what the MOS was.
If you look at the eBay grey-scaled knife and expand the pictures, in the bottom picture you can see where the jigging cut across the remains of the backspring pin. In some of the other pictures you can see bubbles cut by the jigging. Without seeing the knife in hand I can't be sure, but I'd be willing to make a small wager the scales were replaced with some material that was cast in place. I've seen one or two done in a similar manner with JBWeld.
A look inside the frame with all blades open might reveal more information, you'd want to look for the remains of pin holes or pins still in place, or for holes where the scales were pronged on.
