Continuity mistake: When Prue describes the way the warlock Matthew traveled instantaneously, Melinda tells the sisters that it's called blinking, and that Matthew "must have copied it from another witch." But later in the series, every warlock encountered by the Charmed Ones had the ability to blink, and it was considered exclusively a warlock ability, meaning that no witch would have had it. (00:21:30)
Continuity mistake: When Prue lets Matthew out of the locket, the front view Prue has her right hand on her stomach, when the shot changes to the back view her hands are by her side, it does this multiple times.
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