The stamp P choke indicates full choke on many French guns. That said, Ive never seen it on a Darne. The not for ball mark doesnt really tell you the amount of choke, just that it was tight enough that they didnt want you using pumpkin ball slugs in it.
Most Darnes are not marked with actual choke markings, unless they were imported, to be sold, here. Ive seen more than one that had MOD and FULL beaten into the flats, obviously not factory or proof house work, that had chokes that were not mod and full.
My V19 has mod and full on the box it came in, serial numbered to the gun. The gun isnt mod and full. Same with my Italian Richland, although the guy who wrote on the box got one of the two chokes right.

Best,
Ted