Factual error: While Bridger is watching the film of the Mafia boss following Beckerman he signals for the film to be stopped so he can look at the close up shot of the man. He is watching a 16mm film shown through a bog standard projector - stop a film like that for more than two seconds without closing down the projector shutter (this doesn't happen - if it did the screen would darken instantly) and it will melt and catch fire. This doesn't happen.
Factual error: The door of the garage next to the house is of the aluminum up-and-over type, not available until the late 1960's.
Factual error: Lou Erding qualifies his car (42) in third, yet prior to engine startup, the famous "position pole" shows 42 as starting in 20th.
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.
Factual error: The Saint picks up a newspaper, and reads an article that is, according to the headline, about the murder of the Englishman he met the previous night. However, if you actually translate the Italian in the body of the article, it is talking about an industrial fire on a ship.