Continuity mistake: At the start in the van, the girl you see smoking dope hands over her cigarette to the other kid. She uses her index finger and her thumb with the cigarette facing downwards, but in the next shot she has got it between her index finger and middle finger and it is facing upwards. (00:18:35)
Continuity mistake: Part 3 picks up just minutes after Part 2. It shows Jason removing the machete from his shoulder. His flannel shirt sleeves are unbuttoned, whereas they were buttoned up in Part 2.
Continuity mistake: The last thing Andy sees is he walks down the hall on his hands is Jason slicing straight downwards at him with his machete. But this would have bisected him lengthwise, not at the waist. When we see his body up in the rafters, he's been sliced into a top half and a bottom half.
Visible crew/equipment: When Loco is watching the girls swing from a rope in The Barn Loft, he bends down to full with the gas can and when he looks back up she's gone. If you look closely by The Barn Loft door to bottom right there is someone moving with a blue jean leg. Jason is in dark khakis. So this is obviously crew.
Revealing mistake: When Jason is squeezing Rick's head, just before the eyeball 'pops' out for the 3D effect, it's obviously a dummy's head, as the face is wider and slightly larger than that of the actor's.
Revealing mistake: Inside the barn, the webbing that the deer head is covered in is fake, as it 'pulls' like elastic when Shelly moves his along the skull. Real webbing would adhere to his bare skin.
Visible crew/equipment: As Chris rushes across the cabin to slam the open window shut, crew members and monitor equipment are moving around in the reflection of the front windows.
Other mistake: After Jason slashes Andy in the hallway we see the machete ripping down through Andy's abdomen as he is upside down in his handstand. Then his body falls to the floor and Jason starts dragging him, but there is no blood spatter anywhere on Andy's chest, face, or the floor.
Continuity mistake: When Loco goes to the barn, he has a cigarette in his mouth. When he goes into the barn, it has gotten shorter although it's not lit.
Other mistake: When Chris finds Shelly "pretending" to be dead, if you look as she opens the door, you will see the door lock on the knob is outside the door, not inside.
Continuity mistake: Chris puts her lantern down on a table in the sitting room, before going upstairs and finding the flooded bathroom. Later when Rick's body is thrown through the window, the lantern has vanished. (01:08:30 - 01:12:25)
Continuity mistake: When Fox looks up the ladder, we see the edges around the ladder hole, and the floor is covered in hay. Moments later, when Loco looks for her, he climbs up the ladder, and there's no hay around the hole. (00:38:05)
Continuity mistake: When Shelly and Vera are walking out of the store, Vera stuffs Shelly's wallet into her beige pants. Later, while sitting on the dock, she pulls it out of her pink pants. She doesn't have a change of clothes with her. (00:31:05 - 00:56:40)
Other mistake: The whole time Debbie is in the shower, she only washes her chest, arms and stomach. She's always mostly just washing her arms over and over. (01:01:25 - 01:03:45)
Continuity mistake: Jason has dark Khakis throughout the film, until the very end. When the cops are at the house, his body is in the barn wearing blue jeans. In part 4 he is still in blue jeans, but then changes into dark Khakis after leaving the hospital.
Continuity mistake: When Chris is in the sitting room, Rick's body is thrown through the window. When Rick lands on the floor a shard of glass slides down and lies on his cheek. In the next shot it's gone. (01:12:10)
Revealing mistake: When Jason is hitting Ali in the head with a club you see Ali move all three times he is being hit before the club is near him. (00:41:50)
Continuity mistake: When Vera says "I never said you were a nothing." to Shelley you can see Shelley holding the harpoon pointing up. When it cuts he has it lowered out of sight. (00:54:30)
Continuity mistake: When Fox closes the door at the barn we can see she is closing the right door. When it cuts from the inside we can see her closing the left door. (00:36:25)
Answer: The very ending of part 2 proves this, as Ginny appears again found by the police and ambulances. 1) if Jason really got her she would be dead, not alive, he wrapped around her. 2) Paul was dead, not alive and 3) as far as Jason's appearance she would not be able to stand it at first glance, so in her head she would put more human features on his face to be able to deal with it.