Factual error: During Tony's assassination attempt he struggles with one of the "hit men" for control of a pistol. One can see that the pistol does not contain a magazine.This would limit the shooter to 1 shot, providing the pistol is not equipped with a "magazine disconnect" if it is than it can not be fired at all. It seems unlikely that a "hit man" would be so ill prepared.
Visible crew/equipment: Livia and Junior have a chat about Tony while waiting in line for a movie matinee. It then cuts to the Soprano house, and in the next overhead shot of Tony sprawled on his bed, we can see the T-mark on the floor near the door. In a moment, Lilliana knocks and enters to remind Tony of his appointment.
Continuity mistake: At the hospital, when Agent Harris presents his business card in case Tony changes his mind, Harris holds his card at its bottom so it's up over his hand, but in the next shot facing Tony, Harris holds the card at its top so it's below his hand, and it continues this way in the next shot as Carmela takes it from his hand.
Visible crew/equipment: After Paulie and Silvio hug AJ and Meadow at the hospital, when Meadow tells them Tony is with Carmela, we can see the boom pole and mic's moving reflection on the glass, at the top of the screen. Then, as AJ tells Meadow that he doesn't believe it was a carjacking, the mic's reflection dips into view again on the glass.
Visible crew/equipment: While Corrado and Mikey are at Mariolina's wake, just as Corrado says, "Where he spills his guts on some shrink's carpet," we can see the yellow tape mark on the carpet where Corrado had been standing.
Visible crew/equipment: At dinner, when Tony bends down to kiss his mum, the moving boom mic's reflection becomes visible on the glass behind Livia. The reflection of the moving boom pole and mic continues to be seen during the dinner scene.
Visible crew/equipment: When Carmela and the kids exit Tony's room in the hospital, just as Agent Harris walks toward Tony, we can see the reflection of the boom pole and mic on the cabinet glass, near the right side of the screen.
Revealing mistake: When Tony buys the orange juice off the street vendor (just before he is attacked by the hitmen) you can see the magazines on the vendor's stand being blown around by the "heavy winds" that are present throughout the episode. However, if you look behind Tony, you can see the scenery is almost completely still. The "wind" is coming from just off camera. (00:27:17)
Answer: That's not Jimmy, just a look-a-like. Jimmy's short and stout, the guy in "Christopher" episode is tall and medium built. The hair is also different.