Factual error: In the scene where Mulder, the police officer and the doctor are in the doctor's room, the time on the clock reads 8:40. The doctor announces that he going to the bathroom. The scene cuts to him in the bathroom and then back to the doctor's office with Mulder and the police officer. Another cop comes in and says, "Come to the bathroom, something's happened." The clock still reads 8:40.
Factual error: After the agents meet with Kevin's father in the mental institute, Scully lists the medication that he is on: haloperidol, loxapine, and chlorpromazine make sense, but the fourth medication - LARGACTIL - is in error. Not only is it a brand-name of chlorpromazine, but it is not available in the USA, it is a CANADIAN drug.
Factual error: At the beginning of the scene, XO Johanson is looking through the periscope. However, it is nonsense, because the submarine was in silent running, and the Japanese destroyer was circling it, so the sub must have cruised in deep submersion. The water depth there was approx. 270 meters, as the French salvage team claims at the beginning of the episode. There is rarely any significant light beyond 200 meters. Looking through the periscope in these conditions would be completely useless.
Factual error: At the beginning of the "Musings of a Cigarette-Smoking Man" episode Frohike says that the CSM appears when Trotsky was assassinated, i.e. 20 August 1940, but he does not claim that this is an exact date of birth. However, he further says that during the Nazi-Soviet Pact (1939-41) the CSM's father "kept NKVD informed on American plans to enter World War II" and for this reason he was executed before the CSM learned to walk. This means that his father could not have been executed earlier than in 1941. Assuming that babies learn to walk between a few months and 2 years, the CSM could not have been born earlier than in 1939. It means that in 1953 he should have been a young teenager, and not an adult man, as he is presented.
Factual error: Mulder tells Scully that he is trying 27828 and it is not working. It is not surprising that it is not working, because the Napier constant is not 27828, it is 271828. Plus they somehow they know how many digits from this constant should be entered on the keyboards.