Character mistake: In the attic, Melinda Warren is awed at how thick the Book of Shadows has gotten. But according to information from previous episodes, the Book was started after Melinda had died, so she wouldn't know how thick or not it was.
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)
Plot hole: When Prue first releases Matthew, he blinks several times, then blows out the windows and jumps out. Why would he do this and reveal who and what he is when he could have simply blinked? Obviously it was just a way to get the police involved so Andy could be chasing Prue through the episode.
Factual error: In the opening scene in Salem, Melinda Warren is going to be burned at the stake. But in the real Salem trials, no one was burned; all of the people convicted of witchcraft were hanged.
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.
Factual error: Melinda Warren says that after Matthew turned her in to the council, she was burned at the stake for being a witch, except witches were not burned at the stake, they were hanged.
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