User blog comment:Miskos3/Chapter 56, Review/@comment-180.242.210.160-20140407155602/@comment-7418318-20140408091113

Considering how Ymir, Berthold and Rainer seemed to know something about the Beast Titan, I seriously doubt he could be someone from the inner-most wall, in addition to what you already said about the 3DMG.

They all grew up outside the wall, so that's most likely where they have gotten whatever information they were keeping from Eren back then.