Continuity mistake: When Paige follows Phoebe into the kitchen and is trying to convince her that she is telling the truth, Phoebe's right earring is missing in the shots showing both women, but it is there when the shot changes to close ups of Phoebe. It is an awfully large earring to be hidden by her hair in the two-shot. (00:25:20)
Continuity mistake: Paige's headstone reports her year of birth as 1975. But in episode 4-2: "Charmed Again, Part Two," Paige spoke with the nun to whom she was given as an infant on August 2, 1977, and Paige is always described as having been "given up at birth" by Patty and Sam. (00:27:15)
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