Factual error: Virgil's birthdate is given as 1935, but the flashbacks to his childhood have many mid-60's vehicles on the streets.
Factual error: In the 19th Street Parade, it shows the Budweiser Clydesdales pulling their famous wagon. Even though this movie is set in 1897, Budweiser did not start using Clydesdales until April 1933 when the sons gave their father, August Busch Sr., the owner of Budweiser, a 6 team team of Clydesdales to celebrate the end of Prohibition.
Factual error: As director Ronald Neame himself points out in his commentary to the DVD, immediately after Sandy has been heating a piece of bread in the fireplace, she grabs the end of the fork on which it is placed and does not burn herself. (00:19:00)
Factual error: Of all the characters, major and minor, who ever speak German in Switzerland, not one speaks Swiss German. The accents are very different (Swiss German can be almost incomprehensible to speakers of High German), and there's also different vocabulary. While some of the characters might just be non-Swiss speakers of German, at least the underlings at Piz Gloria should be speaking Schwyzerdeutsch.