Almost all of the commendation bars worn by Deputy Chief Gerber above his badge are "fake" bars that are not issued by the New York Police Department.
Gina moves Hitchcock's head from the top of the tree to behind it just by dragging it, as though the tree were a 3D graphic that the image could float around. When using a graphic editing program, the only way to move something behind another element is by changing the layer order, which does not involve dragging it with the mouse.
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.
When Jake takes Holt to the safe house Holt pretends to text his husband and his phone says a little before 6 pm. When Charles shows up a bit later its not even 2 pm.
The ice-rink shown in the cold open is actually that of the Natural History Museum in London that is opened every year in the Winter.
When discussing Charles' injuries, Jake tells Holt that, "Any one of us would've taken that bullet," referring to a singular bullet. Charles was shot twice. Jake should have said, "Any one of us would have taken those bullets."