Horst is seen in 3 different uniforms in the film. During the American Intelligence meeting slide show, he is first show in a Wehrmacht uniform in one photo, then in a party uniform, and when Linda goes to work at his house as a cook, he is wearing and Organization Todt uniform (Third Reich civil and military engineering group). It is highly unlikely he would have switched over to a Civil group well holding rank in the Wehrmacht unless he was as its head and appointed by Hitler. That position was held by Albert Speer.
Just before Ed enters the Customs Hut, his cap displays all of the correct insignia. When he enters, the eagle has disappeared.
Linda states that they heard the radio broadcast telling of the bombing of Pearl Harbor on Sunday morning (they were still in bed in the midst of breakfast dishes), however they were in New York at the time, so it would have been early afternoon New York time.
During World War II the German-Swiss border was closed completely. There were no trains crossing the border during that period like it is portrayed in the movie.
In narration Linda says, "The city was in darkness in preparation for air raids." But when they go in the house and put the lights on there's no blackout curtains on the windows.
Right after Pearl Harbor, Linda's narration says that Ed's real identity as a member of the O.S.S. was revealed when he appeared in uniform. The O.S.S. did not exist before Pearl Harbor and was not officially founded by Donovan and Roosevelt until June 1942. Ed would have worked for any number of government agencies coordinating intelligence info prior to the war, not Donovan, who didn't enter the intelligence game until Roosevelt made him Coordinator of Information in July 1941.
In scene 5 on the DVD (USO dance), Linda's voice-over from the BBC broadcast refers to news of "American boys were being lost by the thousands on Pacific islands with names like Corregidor and Bataan." The latter is a peninsula, and even if she hadn't known it at the time of the "death march", she surely would have done so by the time of the narration decades later.
The flag in Ed's office has 50 stars. It should have 48.
From the very beginning of the war, Ed wears a Combat Infantryman Badge. It was created by the War Department on October 27, 1943.
Franze is going to a concert with Linda. He mentions that the conductor is Herbert Von Karajan. Karajan was born in 1908 and therefore in his mid-thirties during the war. The one in the movie is quite old and has gray hair. In a photo from 1938 Karajan's hair was still jet-black.
During the dance, Ed wears the Army Blue Uniform, which was adopted July 1, 1957, with a Sam Browne belt, which was adopted after 1942.
The steam engine in the movie has a 6-digit number on it's number plate. In the 1940s they had only 5 digits. A leading 6th digit was added to all the serial/registration number around 1960 or even later.
The Wurlitzer jukebox seen several times in the beginning of the movie is a model 1100, made in 1948-1949.
No intelligence agency, no matter how desperate, would send a secretary behind enemy lines with no training, or a senior officer who can't speak the language.
When Ed finds Linda in the laundry basket, he and "Sunflower" clean her up, get her dressed, and give her a pill for the pain. Throughout this scene, she is fairly incoherent, and not wearing any gloves. In the train, Ed notices the bump in her glove and finds the microfilm hidden there. In the closing dialogue from the interview scene, she takes credit for hiding it in there based on another one of her pearls of wisdom from previous Hollywood war/espionage movies. That seems highly unlikely given her state in the earlier scene.
When Linda and Margrete von Eberstein meet at her uncle's Sunflower house, Margrete is thrilled that her father, the Baron von Eberstein, is a friend of Hitler and boasts that the fuhrer has been to their house. She then asks Linda "Would you like to meet the Führer, Lina?". In fact, Margrete admitted that she adored Hitler and it seems impossible that Linda, who was in Germany as a spy against Nazism and against the Hitler, never realized that Margrete was a Nazi sympathizer and could betray her, as in fact happened in the last part of the film.
It made no sense for Ed Leland, who could not speak German, to enter Nazi Germany disguised as a German officer who is mute from a war wound. Aside from the fact that even a mute would be expected to understand and respond to commands or instructions, he could simply have been asked to write out responses in German.
When Linda references The Fighting 69th (1940) she states that it stars Cary Grant and Brenda Marshall, but neither one appears in it.
Linda is supposedly selected for the spy assignment because she speaks German with a Berlin working-class accent. In fact, her German pronunciation is poor and with a strong American accent.
In Ed's office, the translator pronounces "Schornstein" correctly with an "I" sound in the last syllable. Outside, Linda pronounces it incorrectly with an "E" sound.
When Linda goes to work for Franze, her voice over says she's now in a house of the elite where names like Goring, Speer, and Von Stauffenberg topped the guest list. Colonel Claus Von Stauffenberg was not in Hitler's inner circle and at the time of the film he had already joined the resistance and would have most likely been in North Africa. It was not until after his injuries in late 1943 did he go to work as a staff officer to the headquarters of the Ersatzheer ("Replacement Army" - charged with training soldiers to reinforce first line divisions at the front), located on the Bendlerstrasse. There he and the conspirators planned and executed the July 20th assassination attempt on Hitler.