Thread:Koopa422/@comment-1142365-20180804170017/@comment-1142365-20180806235105

Their Quirks should not have the non-canon tag on them either. There is no basis upon which to call them non-canon.

The Oki Mariner Crew and everything else that happens in that episode is canon. It takes place during the Hero Killer Arc and is referenced in the manga. Seijin & Seiai high schools are encountered during the Pro Hero License Exam Arc. In both of these cases, the anime-original content occurs during well-defined places in the timeline of the series. "Presence in the manga" is not a meaningful basis for canonicity, especially that there is a precedent for the anime to introduce its own content, which as far as we know is reviewed by Horikoshi.

Contrast this with the OVAs, which do not take place in well-defined places in the timeline of the series, break the fourth wall to basically tell the audience it's not canon, and are totally disjoint from the rest of the series (with the exception of Tsuyu's family and Habuko Mongoose, which are in a bonus manga chapter). The OVAs thus have a basis for being non-canon - we don't know where they fit in, and are not referenced anywhere else in the universe.