In the swimming pool, Donnie's golden chain disappears and reappears between shots.
The shaving cream on Jilly, who gives Donnie the thumbs up, changes between shots.
At the beginning, the 'Big Boss' arrives in a black Lincoln. From the front first shot, the Lincoln is much older than the model in the next shot, as the car pulls up to the curb. The front turn signals are from both the older Lincoln and the much newer Lincoln.
When Brasco first drives his Cadillac de Ville, it's a 2-door coupe. In later scenes it becomes a 4-door sedan, then back to a 2-door coupe.
Pistone's hair changes between kissing his wife and going up the stairs.
Maggie shovels snow and complains about the cold at the same time that Lefty and Donnie are in Florida, reading John Wayne's obituary. Wayne died June 11, 1979.
During one of Pistone's meetings with other FBI agents at Katz's Delicatessen, several Hasidim are at the restaurant. Katz's is not kosher, so Hasidim would never eat there.
When Lefty makes the coq au vin, he dredges the chicken in flour before browning it (highly unusual and not the classic method, as it often results in blackened flour), then sprinkles a few drops of brandy on the chicken immediately after putting it in the pan (in reality, this is done later, after the chicken has browned on all sides), which results in a flame far too big and too yellow to have been caused by a mere splash of brandy.
Early on, Donnie spends Christmas Day at Lefty's house, then gets into an argument with his wife on Christmas night. The next day, Dec. 26th, he is outside washing the car in a short-sleeved shirt and the upstairs window of the house is open. This would be highly unusual in New Jersey at Christmastime, nor is his breath visible while exerting himself outside, despite historical records showing that it was barely above freezing (32°F) that day.
The FBI never would order an undercover agent to shave because of "regulations." He was playing a character. It's ridiculous.
Sonny Black introduces Donnie to Santo Trafficante as "a friend of ours", it should be "a friend of mine", because Donnie wasn't a made man, only a connected guy as Lefty states earlier in the film. However, in the source material, Joe Pistone noted that Sonny Black did eventually start introducing him, as Donnie Brasco, as "a friend of ours" even though he was not a made man.
In one scene, Donnie answers a landline telephone and the caller asks where he is. This would be quite normal if the caller had been given the number without being told where it was the number for.
When Jilly calls Donnie Brasco into the barber shop, it sounds like he calls him by his real name (Joe) instead of his undercover name (Donnie), but he actually says "Hey! YOU! Come here!".
When Lefty confronts Donnie about the Left Hand being a federal boat, the .38 revolver he brandishes points to the camera, and the blocked barrel is clearly visible.
When Donnie is shooting on the firing range, the second shot ends without the pistol's action returning to firing position because the magazine is empty. The shot cuts to the target, which is immediately struck by more bullets.
In the car, Lefty shows Donnie a newspaper photo of the Carmine Galante crime scene. In the next scene, they pull up to Sonny's club, and small piles of snow are on the sidewalk. Galante was killed in July 1979, so there should be no snow on the ground.
When Brasco calls his family from Miami in 1979, the pay phone is clearly labeled "25 cents for local calls". Local pay phone calls in Florida were 10 cents until 1985.
When Donnie first visits Lefty at his apartment, Lefty is watching a 1990s TV surrounded by blank Beta videotapes.
In an early scene, Neil Diamond's song "Love on the Rocks" plays in the background and a card player sings along. "Love on the Rocks" was released in 1980.
Many 1990s cars and trinkets are visible.
When Santo Trafficante is on the boat talking to Sonny Black, and says "You gotta show a little respect, eh?" his mouth does not match the words he says.
When Brasco tries to call his wife and discovers that the number has been disconnected, he dials area code 212, which is Manhattan. Pistone lives in Clifton, New Jersey; at the time, the area code was 201.
When Sonny hits Nicky (after Nicky makes the "parking meters" remark), he clearly punches him in the forehead, but Nicky grabs his nose as if he's been hit there.