Board Thread:Episode Discussions/@comment-27924662-20170419222535/@comment-2112031-20170421130919

I agree. The argument with Gaiden especially seems weird to me. We barely saw anything of the academy during that story, as it primarily focused on Sarada. Boruto himself barely appeared in it. The idea that Denki, Iwabee and Sumire were just somewhere else during that story is not at all difficult to believe, it's not like we saw the entire class or anything. They could easily add a filler scene with them in it later on when they adapt Gaiden.

Also, the Chunin Exams are optional, not mandatory. Iwabe could have chosen not to compete that year, even if he did graduate at the same time as everyone else.