Factual error: At the end of the report on the findings of the crime scene, the "Italian" inspector tells to his subordinates what literally would translate as "Removes this meddler from here, no more access to the prisoner, that you understand?", which is just wrong in accent, cadence and construct. (00:36:30)
Deliberate mistake: The day of his scheduled departure, Poirot overhears conversations (mainly the one from the window of his room) he couldn't possibly be hearing given the long distance outdoors and the tone of voice. His reactions are shown as if he could hear and not simply see and infer the meaning. (00:23:00)
Revealing mistake: Poirot is sitting reading the paper with the front page visible to the viewer. A breeze ruffles the pages and reveals that the interior pages are blank. (00:14:10)
Factual error: The machine guns on the plane appear to be cannons, which were not introduced until much later.
The Adventure of the Western Star - S2-E9
Character mistake: While handing Mademoiselle Marvelle's letters to Hastings, Poirot calls him "Chief Inspector". (00:06:55)
Factual error: The Jarrow crusade was 5-31 Oct 1936. The sign posted at the hostel stated Poirot was speaking 5 April. (00:15:30)
Continuity mistake: Poirot gnaws the pearls Cornelia returned and deems them to be fake. He indignantly tosses them on the desk, where they show up in the following shot neatly arranged. (01:05:15)
Factual error: The night of the murder, before Jackie has her nervous outburst Ferguson is reading a magazine. It's Life magazine from January 1937 with FDR on the cover. The episode is set in January 1936 (as you can see from the date on Pennington's ticket).
Factual error: When Jacqueline surprises the Doyles revealing her presence on the boat, she was initially covering her face with the December 1938 issue of Vogue. The story is set in January 1936.
Factual error: Poirot gets on the train to London. The engine has an SNCF plaque on it. The video then cuts to the 1936 cycle race. The BCNF was not formed until 1938.
Plot hole: When Poirot and Hastings break into the house, they search the entire house for the box, without success. However, later on, when they are in the kitchen, the housekeeper comes down the stairs - having been lying in wait for them. How did Poirot not run into her when he was initially searching upstairs, particularly when he was making such a thorough search?
The Tragedy at Marsdon Manor - S3-E6
Factual error: It is well established that the episode takes place in 1935 (Nairobi Daily Press dated Saturday July 27 1935, the poster in town advertises the meeting for "Today, Wednesday September 4th", day of the week consistent with the year), but Poirot and Hastings are stopped on their way to the train station by a Wolseley Series II - 14/56, a model that entered production in mid 1936. (00:17:00)
Factual error: At the party, Marcus Hardman tells Bernard that the Countess recently arrived from Russia, and she describes herself as being in exile. Which made sense in the source material, set right after the Russian Revolution, but less sense in this adaptation, set in the mid 1930s. If she stayed in Russia that long, she would have spent 15-20 years with zero privileges from her rank at that point, and nothing from her old wealth, seized by the communist government.
The Tragedy at Marsdon Manor - S3-E6
Plot hole: The murderer is in possession of chloroform from the doctor's cabinet, but there's no realistic timeframe when they could have done it, nor any explanation why the doctor notices it completely at random when Poirot visits, just approaching the medicine cabinet, something he routinely opens and looks through during the day.
The Tragedy at Marsdon Manor - S3-E6
Other mistake: Investigating Poirot's investigation, the clumsy constable crushes a tiny egg under his foot. Poirot crawls to him and points with his cane at the other eggs in the bush. But he points practically at his shoe, and the eggs are in a different spot to the left. (00:20:10)
The Tragedy at Marsdon Manor - S3-E6
Plot hole: The murderer planned everything making it seems accidental. They perfectly managed to fool the coroner and need only to be alone at the mansion to get rid of the murder weapon. So what they do is...they go through great risks to make everyone know someone tried to murder the wife too, making it obvious that there is a killer at large, which only makes the investigation more stringent and most importantly, keeps the police on the premises for surveillance preventing them from disposing of the weapon (like almost everything in this episode's plot it is not a flaw of the original story, but of the dramatization, who added practically every minor character).
Continuity mistake: The Countess arrives at the hotel at the beginning of the episode. In the overhead shot she reaches the top of the stairs with nobody close to her, just the porters behind her, but in the next shot there are other people in the lobby, who at the next cut are even closer to her to fit in frame. (00:02:10)
Continuity mistake: At the end of the 'lovely day' with the Countess, Poirot stops a cab and opens the door for her. Just before the cut, notice a woman with a white dress and a brown hat crossing the street in front of the taxi. The extra crosses the street again in the same direction when he says "Oui" in the following shot. (00:28:50)
Continuity mistake: During the exhibition of the much acclaimed contralto, at one point it is shown that Lady Runcorn is going upstairs and is looking at the smoking person. Back to the host who is on his own at his table. At the first cut, suddenly there are more people standing in attendance in the background (pretty much everyone was seated earlier) and his glass has also refilled. (00:10:15)
The Mystery of the Spanish Chest - S3-E8
Continuity mistake: During the party, the colonel expresses to Poirot his disappointment for the jazz record being played, music "from the inferior races." He puts a tart in his mouth, closing his lips past the piece of fruit. Cut to the wider shot, and he is still holding a tart that sports the strawberry he just chewed on. (00:19:00)
