When Constance walks to the car, she is wearing pointed-toe shoes with a heel. When she arrives at Gosford Park and enters the doorway, she's wearing "flats".
When Lady Trentham is getting ready to leave, she doesn't have a scarf around her neck. When she goes to the vanity, she throws the scarf to Mary, but then, in the next shot, she is taking the scarf off.
When Mrs. Croft and the cook are counting the knives, servants are bringing the candelabra from the dining room down the stairs. Then the gentlemen are in the dining room, where the candelabra are still lit.
Near the end, Rupert and Jeremy are about to drive away, and the cigarette in Rupert's mouth disappears between shots.
When Mable informs Lady Trentham that she doesn't have a lady's maid, Mr. Nesbit lays his tea cup and saucer on the mantel. After the scene cut, when Lady Sylvia joins the group at the table, Freddy again places his cup and saucer on the mantel. In the same cut, a tea cup in the hands of Lady Trentham suddenly appears.
In the song "What a Duke Should Be", the lyrics say, "In B.C. 33 there lived a Roman hero who had shaken hands with Nero." Nero wasn't born until A.D. 54, 86 years later.
Lady Trenthem contends that Ivor Novello's Der Schrecken von London (1927) was a flop. Although Novello humors her by agreeing, the film wasn't a flop. This was done to convey that Trenthem and the other aristocrats are not movie-goers (seeing as how she initially mispronounced it as, "The Dodger").
When the cars meet on the way to the country house, the rain is pouring down from one direction, and the sky is a beautiful blue on the other side of the car. The rain was man-made and not realistic.
The movie takes place in 1932 but some of the songs Ivor Novello sings for the guests didn't come out until years after, like "Glamorous Night" (1935), "Why It Wasn't You" (1937), "I Can Give You a Starlight" (1939) and "Waltz of My Heart" (1939).
The film is set in 1932 but uses a 1934 Rolls-Royce 20/25 GYD48. The Rolls Royce radiator emblem is black to honor Henry Royce, who died in 1933.
The pheasants cluck like chickens.
When Lewis and Probert are listening to the music, the shadow of the camera is visible just before the cut.