Jake and Rosa carry out an investigation involving the Seven-Four, despite the Seven-Four been shut down in Season 4.
While hiding in his office, Rosa overhears Frank O'Sullivan (John C. McGinley) on the phone to his mother telling her that he has acquired front row seats to see Bily Joel in concert. Billy Joel famously insists that the front row seats for his concerts are never made available for sale so they cannot be scalped or acquired on the black market by super rich, unenthusiastic attendees. Instead, Joel has members of his team identify fans during each concert's pre-show and upgrades them to the front row so that it's always the people he considers to be "real fans" that are closest to the stage.
Amy returns from an extended maternity leave once every first responder in New York has been vaccinated. In reality, first responders, especially the police, were among the occupations most resistant to vaccinating, with the police officer's union in NY (and other areas) waging legal battles to bar enforcement of vaccine mandates.
Many of the commendation bars Captain Lamazar wears are "fake" bars that are not issued by the NYPD.
Captain 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.
Santiago's commendation bars are worn out of order, since NYPD regulations requires the American Flag bar to be worn as the highest medal worn.