The automobile bringing Helene to the Bennett home is incorrect - an American model that has its steering wheel on left when England uses right-side steering. Later, the limousine delivering Frank Bennett is correct, with the steering wheel on the right.
When in London in a taxi, Helene says to Henry Thompson "Wasn't there a son?" Thompson replies "Frank, I think his name is. He's in France in the Air Force." The Royal Air Force did not come into existence until 1st April 1918 and was at that time The Royal Flying Corps.