I have a Besson Brevete 1949 Trumpet which seems to have been a model for many modern trumpets..... the serial number is 136xxx.
I appreciate yours is a cornet but from the link
http://www.musictrader.com/besson.html you will see that your horn is probably around 1948.....information is sketchy on these horns but hopefully others will give better information than I can.
Walter