Continuity mistake: After class, when Phoebe is talking to her study group she pulls out the flyer for P3, and in the first shot the flyer is in Phoebe's right hand, but in the next shot she's holding it out in her left hand. (00:01:40)
Continuity mistake: After the manor is broken into, in the following shots while everyone is in the foyer the left front door is wide open in most shots, but in some other shots both front doors are closed during this scene. (00:21:50)
Continuity mistake: When the ani-men break into the manor the entire large center glass of the left door ends up broken, but later while Phoebe is looking for the hydrogen peroxide, Prue notices the front doors and the left door's center glass is intact with only the bottom corner broken. (00:22:00 - 00:27:05)
Continuity mistake: When Prue is sitting at home bored, she spots the vase with the flowers. In one shot the vase is on the left, and in the next shot it's on the right, then Prue moves it to the left.
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