When Perry takes Teddy to see King Kong (1933), the film is being projected in the wrong aspect ratio (1.85 instead of 1.37).
At the end of a day's work, Della's integrated scarf should show creases where it had been properly tied all day. Instead, it appears to be freshly ironed.
When Perry and Delia visit Camilla Nygaard, she does a flip (tumble) turn in the pool as she does her laps. Presuming this is 1933, the year King Kong was released, to which Perry takes his son when he is staying, the flip turn had not yet been invented. Al Vande Weghe introduced it at the 1934 AAU nationals.