When Boy allows Coco Chanel to drive the car, and the car stops, she steps out wearing a white scarf that she wasn't wearing when she got into the car.
Coco Chanel wears a heavy overcoat on the beach in Deauville, looking out on the English Chanel. When Boy joins her moments later, the overcoat is gone.
Etienne wields a polo mallet with his left hand. That's forbidden under modern polo rules, but was allowed at the time of the movie.