About an hour into the film, Hugh Grant (St. Clair) was out and about
in the middle of the night. In one scene, we note one of the nearby
establishments was "open", as we can clearly see by the bright,
red/blue rectangular "open" neon sign over his shoulder. Although a familiar
electric sign is commonly used today by stores and bars, flashy "open" neon signs were just
not used in the 30s, 40s and 50s.
St.Clair Bayfield visits pianist Cosme McMoon in his apartment to discuss the upcoming performance at Carnegie Hall. In one shot, the back of a piece of sheet music on the piano says "The Associated Board of the Royal Schools of Music". In the next shot, the back of the sheet music is different.
After a weekend of golf, St. Clair and Kathleen are in a restaurant. St. Clair holds a cigarette in his left hand. The cigarette moves from his lap to close to his face, and back to his lap.
Toward the end of the film, St Clair is sitting on Florence's bed, consoling her. She starts to cry, and soon tears are running down both cheeks. The camera cuts to St Clair, and when it shifts back to Florence, her face is nearly dry.
The Carnegie Hall concert includes a mixed race audience of servicemen. While the US Armed Forces had limited integration in Europe after the Battle of the Bulge (white officers leading black enlisted men), they remained segregated until the 1950s. If white and black troops had been permitted into the facility at the same time, they wouldn't have been allowed to sit together.
The sailors in the audience at Carnegie Hall would never have worn their hats during the performance. Men removed their hats indoors.
The Columbia record of Lily Pons singing the "Bell Song" from "Lakmé" that is presented to Mme. Jenkins was recorded on November 30, 1944, with conductor Pietro Cimara (not Arturo Toscanini as shown in the film). This was four days after the real Florence Foster Jenkins' death, November 26, 1944.
Arturo Toscanini presents Florence Foster Jenkins with his recording of the "Bell Song" from Leo Delibes' "Lakmé" with soprano Lily Pons, on the Columbia label. Toscanini never performed with Ms. Pons; her usual conductor was her husband, André Kostelanetz. All of Toscanini's commercial recordings were for Victor (later RCA Victor) and its foreign affiliates, or for HMV, aside from two 78 RPM sides for Brunswick in 1926.
Toscanini gratefully accepts $1,000 from Florence Foster Jenkins. In real life, Toscanini would not have been short of money. In the 1940s he lived at Wave Hill, a mansion where Theodore Roosevelt and Mark Twain had lived.
Though Cole Porter was crippled in a horseback riding accident in 1937, and walking was difficult for him after that, he is being assisted by Tallulah Bankhead as he walks into Carnegie Hall.
St. Clair Bayfield smokes filtered cigarettes in several scenes. Marlboro created the first commercially available filtered cigarette in 1922. They were created for women, with filters to keep their fingertips from turning brown and a red butt so their lipstick would not show. Bayfield could have easily gotten filtered cigarettes in 1944.
The U.S. flag flying at Carnegie Hall has 50 stars, although the United States had only 48 states at the time.
The newsstand outside of Florence's building the day after her October 25, 1944 Carnegie Hall performance has on display issues of the March 18, 1946 edition of Life Magazine (with the Eiffel Tower on the cover).
NBC Radio identified itself as "NBC, the National Broadcasting Company", not as the "NBC Radio Network," until sometime after World War II.
When Kathleen turned on the radio in St. Clair's apartment, it came on instantly. It should have needed several seconds to warm up.
The grand piano shown during the final recital in Carnegie Hall is a Model D Steinway piano. It features a modern Steinway & Sons logo, of which the first version wasn't introduced until late 1950s.
Florence designed her costumes in real life, so surely she knows the accessories she wears with each costume. While dressing for the Valkyrie scene she asks for her amulets. St. Clair hands her the armlets that she wears during that performance and announces the correct term.
At the concert, people shout "Bravo!" to Florence Foster Jenkins, and at the end Bayfield salutes her the same way. It should be "Brava!"