As a matter of fact my first gun was a Chapuis O/U 12 GA (I know, I'm ashamed

) and was not proofed.
This was clearly illegal, and the gun was sent back to Chapuis for proofing. This is an exception, and very rare.
The St-Etienne proof house does provide an individual certificate along with the stamping on the action and barrels.
I would be surprised if the Germans did not do the same.
And by the way, it's hard to believe that the german proof house would not stamp anything on the gun.
Could it be that the Blasers exported to the US are not proofed???
Scary thought...
WC