Swiss Expert Needed

[Herb]

I just recieved a Swiss magazine from a gentleman in Norway. It is a very high quality nickel plated magazine with a black plastic bottom. It appears to have never been used. It differs from a regular magazine in that it has a tiny 'lip' extention on the forward mouth of the mag and it weighs slightly more than a normal mag. The back side has a stylized 'P' on it and on the right side of the bottom knob there is a tiny '+' inside the concave surface. According to Costanzo, page 178, item #73, this is a Swiss manufacture magazine proof used on 1929/06 models by Paillard St. Coroix. While checking the Luger Handbook by Aarron Davis, page 30 he indicates that the 1906/29 was a special assembly presentation piece and only three are know to exist. Surely I haven't stumbled onto one of only three, what is the real story here? 1929/06 vs: 1906/29? Nearly forgot-it has the old style round spring, not the newer zig zag type.