Miss Fred's hairstyle throughout the film and costumes during the fashion parade are from the 1960s-70s rather than 1940.
Early on the girls are stopped at a German vehicle checkpoint. One of the German vehicles is a Steyr 1500A. While authentic for WW2 generally these did not go into production until 1941 and thus would not be seen in France in the summer of 1940.
In a shot of the action on the airfield, the shadow of the camera crew can be seen in the foreground.