Board Thread:False Info and Speculative Discussion/@comment-26781694-20160309171151/@comment-26879545-20160518212445

@Levii:

If you recall, there's a bit in Dreamcatchers where Liam brought Mason to a pack meeting and Stiles told him "We told you that you could tell him (about the supernatural); not invite him into the inner circle."

Mason wasn't always part of the pack. In fact, he asked if he was "in the inner circle" and Liam and Stiles told him that he wasn't. That was in 5a, IIRC. Skip to the "Escape from Eichen" plan and Mason was a key part to the "escape" part of the plan.

Some time between being told he wasn't in the inner circle, to his role in "Escape from Eichen," he became a pack member. If I had to guess, I'd wager it happened the night he stopped Liam from killing Scott in the library.