Other mistake: They keep saying the taxi cab is 20 years old, but that cab is brand-new in the episode.
The Daughter of Autolycus - S4-E5
Other mistake: Lady Felicia says "Ah, Father, how very propitious." The subtitles say "Ah, Father, how very capricious." (00:03:10)
The Patience of Maigret - S1-E1
Other mistake: A newspaper headline reads "MAIGRET tient t'il enfin le tueur?" This makes no sense in French. It should read "MAIGRET tient-il enfin le tueur?" ("Does Maigret have the killer at last?"). (00:27:55)