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)
Plot hole: In 'Centennial Charmed' Paige orbs to another reality where she loses all her powers. Leo tells her the this is because she was never called as a witch in this world, but Paige had most of her powers before she was called because of her whitelighter blood, so she should retain these. Leo says that Paige has assumed the life of this reality's Paige, but then adds "...or at least the life she would have lived if she hadn't been killed". If alternate Paige had lived she would have had Whitelighter powers, even if she didn't know about them, so our Paige should also have them. (00:28:00)
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