Board Thread:Questions and Answers/@comment-16461120-20160405223613/@comment-3406131-20160412170058

I come late here, but, while I don't really care, I think:
 * Vision, then the Twins, were kind of "de facto" members during the battle of Sokovia. I know the Avengers are an official thing from the beginning on Earth-199999 (Avengers Initiative, SHIELD, the World Security Council, etc.), but when they assembled against Loki, they actually weren't something else than a group of heroes banded together, and not under the official warrant of anybody.
 * That said, the creator's comment isn't here a really good argument because it may mean Avenger as "a classic character generally recognized as an Avenger" or a "proper Avenger", or even an Avenger by the philosophical meaning from the first Avengers movie.