Continuity mistake: When Prue runs into Susan Trudeau at the restaurant, she asks if she's Andy's sister, only to find she's his ex-wife. But Prue knew Andy all through high school - she would have known he didn't have a sister. (00:12:25)
Visible crew/equipment: When Piper is taken by Wong's men Mark shouts for help, and just as Prue tells Phoebe to call 911 from the car, the blue tape mark is visible on the rug beside the table, where the sisters had been standing before rushing out. (00:36:05)
Visible crew/equipment: When Prue is flicking through TV channels, just as Phoebe walks into the bedroom and stands beside her sister, we can see the movement of the camera operator and camera in the reflection within the standing mirror, near the door. (00:34:05)
Visible crew/equipment: After Piper takes the picture of Tony Wong holding the newspaper, when she and Mark quickly drive off, we can see the actors' large yellow T-mark taped to the ground near Wong and his men. (00:28:35)
Other mistake: When Piper and Mark are in the police parking lot she holds the door open for him to get into her SUV. When he gets in you can see the SUV go down from his weight in the vehicle. Ghosts are supposed to be weightless.
Revealing mistake: When Mark (as a ghost) and Piper leave the hotel after he asks for her and Phoebe's help, he bumps into the handrail as he walks down the steps.
Chosen answer: Her agent/manager negotiated a special billing as part of her contract. It distinguishes her from the rest of the cast, probably when she became a producer on the show.
JC Fernandez