The gold bars on the front of Terry's suspenders repeatedly move up and down between shots.
Amy instantly knocks out both Jake and Charles with a rag soaked in chloroform. In reality, chloroform takes several minutes to render a person unconscious.
Gina pulls her "you just drank cement!" prank on the squad one last time, but they are drinking from clear glasses that are filled with a clear, yellowish liquid.
Deputy Chief Ed Williams is not wearing his American Flag commendation bar as his highest bar as required by New York Police Department regulations. Also, most of the commendation bars he wears are "fake" and not issued by the NYPD.
Deputy Commissioner Holt wears his Commendation breast bar above his World Trade Center Breast Bar. When the WTC bar is worn, it is worn above all other medals, but below the American Flag bar.
About 18 minutes in, when the squad returns to the precinct bullpen, the chair in the middle of the floor is empty. When the camera cuts to the squad and back to the chair, suddenly Hitchcock's legs are visible just before he spins around to reveal that he has won the heist.
During the "previously on" recap, the shot of Jake saying that he's leaving the 9-9 is mirror-flipped.
The squad leaves the bullpen empty, save for the janitor. There is a night shift that should still be working at that time.
Jake plans to let everyone, including Captain Holt and incoming Captain Jeffords, that he is resigning and the heist day is his last day. A detective resigning on good terms would require a longer notification period than same-day.
Hitchcock reveals that he never really left the 9-9 or retired. As Holt is his superior officer and captain of the precinct, he would know who is still assigned to the staff there. If Hitchcock never retired, he would still be on the roster and payroll.