Found a nice website addressing postwar German proofing. You will see that the later postwar proofs match the earlier prewar one which may indeed create confusion.
http://www.waffeninfo.net/beschuss.php
Also follow the link to the german proof house identifiers. The staghorn is found on postwar Mauser Parabellums and I have a 1989-proofed VoPo which has the Koln proof mark.
http://www.waffeninfo.net/waffen/bes...schuss_brd.jpg
Proof mark years are either 2 letter year codes or 2 digit year codes (i.e. 1972 is proofed as 72).
The year letters follow the following scheme:
A = 0
B = 1
C = 2
D = 3
E = 4
F = 5
G = 6
H = 7
I = 8
J = 9
So 1989 would be represented by IJ.
Hope this may clarify some proofmark issues.