Someone has attempted to defile the 65mm chamber markings, but, they are still visible. They also did a piss poor job of marking it 70, for 2 3/4” chambers. I’m sure they have been let out. Not typically a problem on a French gun. I see no poor attempts at action tightening in the photos.
The gun is a 16, not a 20, as witnessed by the 17.0mm stamps of the barrels. The Shooting Stars are likely a grade marking of some sort, not one I am familiar with. It was proofed in a finished state with French smokeless powder T, post 1900. It was double proofed, a higher level than single proof. Both are stout levels of proof. Acier Special just means special steel, not anything significant from where we are today, in steel making.
I can’t make out any of the other marks, but, it likely doesn’t matter. If I needed a 16 beater, I might try to take up the slack in the action with a .004 brass shim on the hook, you could try a piece of typing paper, and see if it helped, at the gun shop, but, it would have to be cheap if I was going to do that.
Best,
Ted