On his trip through the countryside when Reynolds stops to load gasoline, the lights of the pumps are on and in the next shot, off. Also by the ambient light it is evident that it was filmed at two different times of the day.
When Alma takes off her shoes in Woodcock's bedroom, she leaves them by the door. When Cyril enters the room, she steps over the shoes, but when Cyril leaves, the shoes have changed position and Cyril also seems to trip over them.
When the countess tries the dress she puts her glasses on to take a look in the mirror. The next shot Reynolds is approaching her and she is wearing no glasses.
When Reynolds is shown leaving a room at the start of the film, he puts a cigar to his mouth. In the next shot with him on the other side of the door, the cigar has immediately vanished.
When Reynolds is having breakfast at the Victoria Hotel, the 2 cords of the sun blinds next to him change position.
Cyril tells the ladies repairing the wedding dress that it must be ready to be sent to Belgium by 9 the next morning, implying that it will be shipped like a regular package. As the dress is custom-made (and for a princess, no less), in real life, Cyril would have been packing her bags in order to deliver the dress herself; also, to ensure that it fits on the princess perfectly.
When Reynolds is driving Alma down a dark country road at night on their way to dinner together (16:39) the trees become lit behind the car, as if the headlights were in the rear of the vehicle.
In the credits the character of Rubio Guerrero is spelled "Rubio Gurrerro".
During Alma's "noisy" breakfast, she lifts the coffeepot to pour, while her other hand physically steadies the teapot. As it is made of silver, if the coffee or tea inside were hot, the pot would be physically too hot to touch.
Although the film is supposedly set in 1953-1954, the Bristol 405 that Reynolds Woodcock drives around Whitby was not manufactured until 1955.
In fact, the film is set in '55, according to P.T. Anderson.
In fact, the film is set in '55, according to P.T. Anderson.
When the countess arrives at the front door, the door knocker is heard so Cyril goes to open the door. The countess is climbing the steps and no one else is at the door to do the door knocking when Cyril opens the door. It is clear that someone with the countess knocked on the door and then walked back to the countess to ensure she would be the first to cross the threshold.
Very wrong, there appears to be no cigarette smoking in 1950s London fashion industry. Inconceivably, none of the models smoke, nor do the royals and Alma. Nor does anyone smoke at the New Years and wedding parties.
When Alma first sees Reynolds in the Hotel dining room, she trips. That was a genuine mistake. Vicky tripped on lighting cables, but PTA decided to keep it in the film.
At the end of Reynolds' and Alma's wedding the vicar says, "You may now kiss the bride." No-one says this at a British wedding, least of all in the 1950's. It is an American custom only (especially common in American films probably).
A character says, "I don't mean to be racist..." That word didn't exist, at least in British English, in the 1950s. Someone might have used "racialist".
During a scene set in a hotel room a modern blue "Fire door keep shut" sign can be seen on a door in the background.