Board Thread:Questions and Answers/@comment-39941225-20200606234716/@comment-25933225-20200607164728

The training chapters, in the manga, are after the Trost arc, as flashbacks. Isayama made this choice back then (instead of putting the training chapters after the fall of Shiganshina) because his manga just started, and he didn't want to lose his first readers by having 3/4 chapters of training. He prefered to go directly in the Trost arc (that begins at chapter 4 I think). When he ended the Trost arc, as he had enough readers, he gave training chapters.