In the taxicab, when Coco tells Dr. Topaze of her adultery, the back projection shows cars during daylight. But before she and Topaze took the cab it was clearly night.
Early in the film, a student tears a page from a wall calendar, revealing the date to be 1932, December, Friday the 13th. In actuality, the 13th of December, 1932 was a Tuesday, not a Friday.
In the taxi-cab just as Coco tells Topaze about her adultery with the Baron, there is an awkward splice in the rear projection footage making cars and people on the street disappear momentarily.