Board Thread:Questions and Answers/@comment-16461120-20160405223613/@comment-4651179-20161003033418

Necroposting in order to bring up to this dicussion a fact that was considered by Nausiated in this comment but couldn't be taken into account until now: the guidebook's stance.

The recently-released Guidebook to the Marvel Cinematic Universe - Marvel's Avengers: Age of Ultron includes Quicksilver in a headshot list of Avengers members.

However, it's worth noting that in the Avengers bio, Wanda is mentioned as a new recruit only together with War Machine, Vision and Falcon. Additionally, Pietro's bio comments that he "joined Wanda, the Vision, and the Avengers in Sokovia to make a final stand against Ultron" and refers to the group as "Pietro and his allies." On the other hand, when the text is talking about Wanda and Pietro and moves into the other heroes, it refers to the core members as "the other Avengers," which could imply Wanda and Pietro are considered such.