The Grand Prix 1900 means "Grand Prize 1900". They had regular expositions that were juried back then. Makers would submit their work. This model won the 1900 Grand Prize, most likely in Paris.

The Not for Ball is another way of saying the barrels are choked.

As Larry stated, they could use various powders for proof. I seem to recall that T produced higher pressures.

You can download the French proof marks here:
http://www.damascus-barrels.com/files/Damascus-Barrels_dot_com_French_Proofmarks.pdf

Pete

http://www.damascus-barrels.com/Movie.html