User blog comment:San&Ashitaka/Chapter 57 review/@comment-93.209.37.150-20140506162513/@comment-13234254-20140508171504

About that Ymir thing. Well, it's actually kind of clear that at least Hange, i don't know about Erwin, but i think he didn't have any knowledge of her name before the revelation of her being shifter, didn't know of Ymir until the conversation she had in chapter 37 with minister Nickolas, when Eren, Mikasa and Armin realizing that the girl the late minister refered to was Historia ( then known as Krista ) and the trio trying to explain to Hange who that girl is said, it was Mikasa who said that if i recall correctly, it is the girl who always stays ckose to Ymir with Hange being like What? Ymir? So, i think that pretty much indicates that even though Erwin, Levi and Hange did know about the contents of Ylse's diary, none of them knew about that Ymir was in the Legion, or even who Ymir is.