Wade,
I think the number on your 1946 CP box should be stamped on the main casing not the mid cover (as per first picture).
Later CP boxes were stamped on the middle cover as per my 1949 NH (picture 2)
The numbering in the first picture is for October 1946 i.e.
G6 (NH or NG)
K (10th month)
46 (year stamp) and mine is for April 1949. So I think what you need is an unstamped middle cover (or polish out the stamp on your current cover) and stamp a new number on your main casing. If you know your month of despatch you can stamp the corresponding month code as well i.e.
A=January,
B=February ...
M=December (
"I" was not used).
Pete