When Charles is getting his wedding attire one of the outfits he picks out is a kilt and Jake tells him he isn't Scottish. In a later episode Charles says that hes cousins with Susan Boyle who is Scottish.
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.
Officer Deetmore wears 2 fake commendation bars that are not issued by the New York Police Department. One actually appears to be a ribbon from the US Air Force (which is not allowed to be worn by NYPD regulations).
In a flashback from the 70s Scully and Hitchcock are their normal selves trying to go on a diet. But in Hitchcock & Scully (2019), they are presented like gym freaks.