Continuity mistake: The last time Shakes serves as an altar boy for Father Bobby, he puts the white coat on top of the black gown, and it is all straight. Yet, when he turns to Father Bobby, the coat is lopsided and hangs over his left shoulder, and Father Bobby straightens it again. Even if the coat slides a little when Shakes leans towards the mirror right before turning to Father Bobby, it wouldn't pass his shoulder unless he did it on purpose.
Continuity mistake: When young Shakes is running away from the hot dog vendor, he has the hot dogs in his hand and doesn't toss it away before he meet up with his friends, yet there is a shot in between where we can see him running with empty hands.
Continuity mistake: On the subway, the background is shifting as we see through the window when Michael is in focus. Yet, these shots are inter-cut with shots focusing on Carol. In some of these shots, the background is all the same.
Deliberate mistake: In the scene where the boys scratch off the paint on the window so they can look at the ice skaters getting dressed, there's a grille about 6 inches from the window. When viewed from outside their faces are pressed against the grille, but when the shot changes to inside the building looking at their eyes moving, their eyes are much closer to the window than the grille would allow.
Other mistake: In the scene where John and Tommy are in McHale's Bar in 1981, John offers Tommy a cigarette from a Marlboro cigarette box. However, when Tommy puts it into his mouth to light it, you can see a small camel on top of the cigarette.
Continuity mistake: When Michael and Carol are talking on the subway, Michael reaches out and begins touching/stroking Carol's hair. But in the reverse shots of her, his arm and hand, which should be visible over her shoulder, are nowhere to be seen.
Plot hole: In the scene where Lorenzo gives the evidence to the policeman (in the back of King Benny's policeman-nephew's car), he gives him a gun with shell casings and Adam Styler's prints on the gun. Where exactly did he procure these items?