In this close up you can see the unusual seaming. The curved seam goes across the back as well, which you may be able to see in the back shot above. Not easy as the matching of plaid is perfect.
I found the Gay Giano website and it says its customers are "trendy customers, celebrities and artists." !! The Cour Carre customer is the modern professional and business executive.
Birgitte asked on my last post "I'm also SO intrigued by the three piece sleeve, and think the stars have aligned: I"m just starting on a Chanel-inspired jacket. Do you think this is the 'famous' sleeve and vent referred to in the Threads article? If so, could you be super duper kind and show the underside of the sleeve, pretty pretty please!!! " And yes I think it is! I just had a look at a Claire Shaefer pattern with the three piece sleeve and it looks the same. The seam up the middle matches the shoulder and there are two seams under the arm. Here is a picture of the sleeve up: