In November 1957, Ed reminds his boss that he cited Carmine for speeding "six months ago" but that scene was set in October 1956, 13 months earlier.
The calendar page on the wall next to Ed's desk is correct for the first scene, but it does not change for the rest of the movie despite the passage of over a year.
In 1957, Joe (Joe the Barber) Barbara wasn't a young wiseguy looking to be "bumped up," as depicted in the movie. He was 52 years old and was the boss of northeastern Pennsylvania.
The baseball results announced on the radio along with the news of the shooting of Frank Costello is actually for a game that happened four days later, which is strange because the screenwriter would have had to look it up and obviously knew the correct date of the shooting, yet somehow chose the wrong date for the baseball game.
Ed picks up Natalie at 6pm for a dinner date in November but there is sunlight in the windows while they're at the restaurant. Sunset in November in upstate New York is before 5pm, so it should have been full dark outside.
The state police have baton rings made for "side-handle batons" which were not available until the 1970's. A baton ring for a side-handle baton has a protrusion to keep the baton's side-handle from rotating outward when worn on the belt.
The day before the meeting November 14 all of the outdoor photography reveal the leaves on the trees are all green. By that date all of the remaining leaves would be in their fall colors of red, yellow or brown. That part of NY state is known for the brilliant tree colors in the fall.
A stock shot inserted during scenes set in late 1957 include the marquee of the Winter Garden Theater listing a play that closed in 1956.
While Croswell is staking out the Barbara house, during a radio conversation he has with Lane, a "roger beep" is heard at the end of one of Lane's transmissions, indicating that the actors in the scene are communicating using modern radio equipment.
Though the setting for the movie is up to November, 1957, the flag on top of the sheriff's is a 50 star flag, which did not come into being until July 4, 1960. Instead, for 1957, the flag should have been a 48 star flag.