No big deal. You have to look at all the marks to date the proof. Pre-1924 guns are difficult to pin down to an exact year. The Belgian proof system was the most "expressive". It also can be very confusing. The real nightmare comes when a gun was resubmitted to the proof house.
On Belgian guns, look to the gauge mark and you will immediately get a "feel" for the time frame. You can almost be certain it was not done during the war years. Although even that is not an absolute.
It seems like a decent field gun. If it checks out, it would be fun to shoot with reasonable loads.
Pete
