That's the first I've heard of Charbonneaux ever farming out his designs to other designers. I don't know the source on that info but it seems a little suspect to me.
Was Paul Bracq instructed to create a design that looked like a 'typical Charbonneax design'?
I'm not saying this is definitely untrue, I don't have access to the Charbonneaux book where I'm sure the answer lies, but I would need some more information before I totally believed this!