Factual error: There are many factors concerning Niles' post-operative state which are very inaccurate. After open heart surgery it takes at least three months for the chest bone to heal, Niles would not be able to drive a car for weeks, nor would he be able to lift or twist which he does on the show. Also, he doesn't sport a scar. Your chest bone begins very high up, just below your neck, his scar should have been visible on numerous occasions.
Factual error: This episode takes place on Frasier's birthday - Martin had ordered a copy of the newspaper published the day Frasier was born and it is sitting on the dining room table when Daphne glances at it and says "Queen Elizabeth's had another baby." - in the Episode The Late Dr. Crane earlier in the same season, Frasier was mistakenly reported as dead on a local TV news show. The dates for his life were shown on the show as 1952-1999. The Queen, in fact, did not have a baby in 1952.
Factual error: Simon, having just been kicked out of Frasier's apartment, is trying to convince Roz to let him stay at hers. In the background the set shows a wharf area with at least one tall ship, Alito's Restaurant, Pier 45 Shed A, and Fisherman's Grotto. These are all located at Fisherman's Wharf in San Francisco, not Seattle.
Factual error: At the cafe, the employee says that Niles' credit card was declined at the register because "cancelled by order of co-signatory." A co-signatory shouldn't be able to cancel the card without the other person.