Revealing mistake: The establishing shot of Boston General Hospital at The End of the episode shows the same porte-cochère that was used for the BYU Medical Center in Provo, Utah eight episodes earlier in "Roadrunners." It appears they just digitally inserted this portion of the building over different facades. (00:40:00)
Suggested correction: These are two different porticos. The columns in the Boston picture show concentric grooves, and the fascia on the front of the roof structure is smooth and rounded. The Provo portico has smooth columns and the front fascia is composed of flat rectangular panels. In both pictures the porticos seem to be well-matched to the building structure and landscaping. It's unlikely that the production would have gone to the considerable expense (in the 1990's!) of a digital enhancement.
I could have worded the entry better, but while it's not the exact same portico, it appears to be the same building, but different entrances. The two structures have the exact same kind of writing on the right side and the overall design of the structures is remarkably similar, with some subtle differences in the columns and fascia, as you pointed out. Seems highly Improbable that a building in Boston and another in Utah that are not supposed to be affiliated with each other would look so alike.
It's also worth pointing out that the shot of the BYU Medical Center from Roadrunners showed the Kansas state flag flying outside the building, suggesting that the crew either had stock footage of the building, or they happened to be in Kansas and filmed the building in question. It's highly unlikely they went to the effort to find stock footage or actually went to a different building with a similar looking portico for the sole purpose of using it as an establishing shot of a different hospital in another episode.
After studying the photos again, I would have to agree that it is probably the same building, probably with an addition added to closely match the original construction. As to the improbability of two hospital architectures being so similar, I would reply that this may be common. I had occasion in the 90s to visit a hospital in East Lansing Michigan and later one in Alexandria Virginia that were virtually identical and owned by different health care systems.
Revealing mistake: In the opening sequence, a man who is hallucinating badly is apprehended by the police. They find a dead blonde woman in the trunk of the man's car. In a close-up of the dead woman, all the dried blood on her face is an added digital effect; however, the dried blood "drifts" around, seemingly out-of-sync with the video. Similar "drifting" digital effect problems are seen in other X-Files episodes.
Revealing mistake: As Dana Scully is examining the dead woman found in bed with Skinner, she observes a strange luminescent glow on the woman's nose and lips. It's apparent that this glow was added digitally; but the digital effect is "drifting" around the dead woman's face, seemingly out of sync with the video. Similar "drifting" digital effect problems are seen in other X-Files episodes.
Musings of a Cigarette-Smoking Man - S4-E7
Factual error: In the US classified information system there is "compartmented information", but there's no "compartmentalised information." (00:08:00)
The Sixth Extinction (2) - S7-E1
Factual error: When Skinner is at Kritschgau's apartment building, the time stamp onscreen says it's 5:05 AM, but when Kritschgau answers his door, he says it's 6:00 in the morning. Plus it is shown to be broad daylight outside. The sun is never up that early in Washington, D.C. (00:15:55)
Factual error: Skinner says that he could not print the file. However, Scully somehow must have been able to print it in order to give a hard copy to Albert Holsteen for his translation. (00:26:35)
Anasazi (1) - S2-E25
Factual error: It is completely impossible the Thinker has made a digital copy that cannot be duplicated.
Continuity mistake: When the nurse takes off the bedding, the sheet is crumpled, but in the next shot it is suddenly pretty straightened and smooth. (00:02:50)
Unrequited - S4-E16
Revealing mistake: The handle and latch next to the supposedly working intercom on the chain-link security gate entrance to the "White Hand" facility is obviously non-functioning - when the gate is opened it can be seen there are no functional operating parts. (00:08:40 - 00:09:15)
Never Again - S4-E13
Factual error: The first time we see Ed's tattoo, it is supposed to have been freshly done and he even removes the new bandage. However, there is no blood or excess ink on his arm, no redness around the lines, no swelling at all; no way at all that it could be a fresh tattoo.
The Sixth Extinction (2) - S7-E1
Character mistake: When Scully is reviewing part of the translation she has made of the alien artifact, there are four amino acids that she has written: Ademine, cytosine, thymine and guanine. Ademine is misspelled. It should be adenine. (00:23:10)
The Field Where I Died - S4-E5
Continuity mistake: When Scully is searching through the pictures to find Sarah Kavanaugh and Sullivan Biddle, she turns the photographs over and they have a label on them to say who they are. Yet when the shot changes angle to show the photos from the back, the labels have disappeared.
Continuity mistake: During the shootout in the warehouse, a wedding ring is visible on Mulder's finger. While it's possible Mulder was married before, the Lone Gunmen are shown hacking into Mulder's FBI dossier and Langly reads out that he is single.
Revealing mistake: When the dad and Charlie are eating their ice cream cones at The Beginning of the episode of the episode you can tell that the ice cream is fake.
Factual error: When Suzanne Modeski retreats to the restroom with a pair of pliers to pull out her tooth, she is only gone for approximately 15 seconds before the gunmen follow her. For a petite woman to rip out a strong, healthy molar from her own mouth (which also had metal prongs Underneath in her gum) would not take so little time, no matter how determined she was. It's also highly unlikely that the lack of anaesthetic would have allowed her to do so without making pained noises.
