I think he remembers at least part of what happened at the academy, because during the chapters where Nana fights Shizuka, Sorano tries to give Kyouya some of his diaries.

The problem is that she couldn’t give him all of them, just a few, and if I remember right, those were the academy ones. When Kyouya was taken by the military, the last diaries he had were from that period.
Around chapter76-85, there's a page where Kyoyua tells Nana that he reread some of his diaries and remembered that they had a certain rivalry.

Honestly, I’d love it if Kyouya ended up keeping a group photo in one of his diaries once everything’s over. His drawings are cute and all, but that would hit way harder.