Continuity mistake: When Carter is in the interview room with Allen he looks at the clock and it reads 09.30am after Regan releases him Regan goes to the Sweeney office and sits at his desk, Carter looks at his watch and it says 09.00. (00:54:10 - 00:58:30)
Continuity mistake: When fighting with Allen in the boat scene, Regan has two right arms. In shots where Regan's face appears, he has a gun in his right hand with which he hits Allen. In shots where Allen's face appears, Allen's neck is held by Regan's right hand too. (01:40:30 - 01:42:00)
Answer: Yes it was actually used in the film.