Revealing mistake: When the sisters are talking in the kitchen about Phoebe crashing Prue's car, whenever Phoebe turns around you can see a distinctly grey patch of skin on her shoulder where one of the actress's tattoos is covered up.
Continuity mistake: Phoebe had to touch both Jane and Malcolm for them to be trapped in the painting, so how come she didn't have to touch Piper and Prue for them to all be freed? (00:39:25)
Continuity mistake: When Piper writes the name "Nell" backwards on the castle window she uses two fingers so each letter is doubled lined, but when the name is viewed from the outside all the letters are single lined. Additionally, after she writes the backwards "N" on the bottom right window, in the next closeup of the swords' pointy ends that window is blank. (00:30:20)
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