Questions about a 1929 Swiss Military

[P. Octo]

Learned gentlemen, here are my questions. I have a beautiful 1929 Swiss Military Lüger and I have found all the necessary references to identify it in Aaron Davis's book "The Standard Catalog of Lüger", page 157. Number fits.
But there are 4 discrepancies:
What is the mark on the back of the receiver?
Is the mark Left Front that of colonel Muhlemann?
Why a "P" on the front of the receiver?
Why a U notch when all the litterature tells of a V notch?
I am relying on your exoertise to enlighten me.
Those questions aside, it shoots beautifully and has a trigger of almost Benchrest quality.
Thank you in advance.