Are there any numbers in front of the barrel flats that could be bore and choke diameter in MM? You'll often find them on Belgian guns.
Quite a few of the Belgian date codes can be a bit tricky to decipher. The rho can sometimes be confused with a script p (1937). But in any case, you're relatively modern (post-1924) with the 16/70. 5.25 is definitely on the light side for a 16. And even though France had a thriving gun industry of its own, not at all unusual to run across Belgian imports that were sold there.
