Barbara arrives at the Stork Club with Brooks, but without her purple wrap, which was wet when she was playing with Tony in the bathtub. When they leave, she is wearing it.
In all the shots in the opening 1946 sequence of the Baekelands smoking around the infant Tony's cradle, the smoke always disappears in close-ups of him (the film-makers have clearly been careful to keep smoke away from the baby).
When Barbara and Tony first walk through the park in Paris, they pass a little girl, and a young woman walks into frame towards them. In the next shot, the little girl is in a different position and the young woman is gone.
When Tony meets Blanca on the beach, he first talks to Jake. As Tony and Blanca chat, and she decides to turn on her radio, a woman inexplicably appears on Tony's immediate left, as though she knows them. When Blanca starts dancing in front of Tony, the other woman is gone.
In the opening scene, when Barbara arranges a dinner date at a restaurant, a pimple is between her cheek and her chin. It disappears mid-scene.
The ambulance at the end of the film is a mid-1970s Chevrolet van, which were not used in London.
At 55:08, which is set in the year 1967, there is a modern-day motion detector on the outside gate of the house. It's on the rock wall directly above the wrought-iron gate.
While Barbara and Antony are sitting in a bistro, she attributes the quote "when a man is tired of Paris he is tired of life" to Fitzgerald or Hemingway. The correct quote is "when a man is tired of London he is tired of life", by Samuel Johnson.