Poirot and Hastings drive up to the apartment building in an open wheeled roadster, when they arrive, Porot gets out walks up to the door and looks back at Hastngs who is sitting in a completely different car with fully fendered wheels.
When Mrs Daniels leaves home followed by Hastings, both cars go over a speed bump, which weren't introduced to the UK before the 1970s.
When Mrs Daniels slips her car into a side turning whilst being persuade by Hastings white fumes are seen coming from the exhaust. This only happens when a car has been recently started up and not after having been driven for a long period.
Poirot arrives in the government office at noon, talks with the government officials for less than five minutes, but when he looks at his watch he says its five-fifteen which is impossible.