Board Thread:Speculation House/@comment-35979206-20181021114251/@comment-26397825-20181022115424

No Maidens were made after V2 was finished, between volumes. In fact, it was only made a proper thing after Monty died. He went to Miles and Kerry and said "I have a cool idea" and then when he died they felt they had to add in this super cool thing that he had been super excited about. Not to mention that Raven was introduced partway (about 3/4) through the season, not at the tail end of it.

In other words, Raven was introduced before Monty had the Maiden idea and it was implemented after his death. Ergo, her mask was retroactively made to be a cover for her Maiden powers.