I have looked up a lot of SS Dagger numbers with my SS Officer Research project and this is the first one I have seen numbered on the tang nut. Also, it is a bonus to have the initials engraved. Just a great one.
The only other unusual M36 addition that I have seen with an unusual add is one with two small metal pegs in the bottom of the lower crossguard to hold the knot away from the scabbard throat when the dagger was inserted into the scabbard (also a professional period addition on a direct veteran acquired piece).
