@Rodolphe de Lera
No worries - It is an OK number.
It is a strange number because it is for the body ONLY and is not a Vehicle Information Number ( VIN ) for the entire car.
The CMC "Certificate of Origin" number you show was often (but not always) attached to the car either in the front storage compartment or inside of the driver's door opening. Most governments do not use that number for anything. It tells us that you have a "Classic-side" car body (like an original 356) and that it was the 11XX order taken for that model by CMC. That's all. As an example, here is my CMC plate, telling us that I have a "Speedster Californian" which has wider fenders than your car:
If you want to see the original VW VIN, then look on top of the center tunnel right behind the seats. Lift up the carpet and the car's VIN should be stamped permanently into the top of the tunnel, but it may be hard to read because of age. Use some light sand paper to make the numbers stand out.
I hope that this helps, and have a wonderful day in France!