Board Thread:Consensus Track/@comment-4521917-20150810051444/@comment-28861328-20150902005223

Shock Dragoon wrote: From what I remember the Hiden (and Shiden for that matter) were worked on by the authors with heavy involvement from Kishi. So that would make them as close to canon as possible. However, it appears that they are left up to read interpretation as well so it can go either way.

Regardless, given Kishi was involved with their creation doing illustrations for them, he reviewed them and gave the seal of approval, these books are as canon as we're gonna get for a Part III since the next Gen is Part IV so I'd vote "as close to canon as we can get"

By the Nine, there is No. Part. III. None. It doesn't exist. It never shall. Part IV doesn't exist either. They don't. Kishi said Boruto: Naruto the Movie was the best writing he could give to the series so that pretty much confirms he's done with it. The anime could go on for the next 10 years for all we care, and there would still never be a Part III.

Part I and II were named such by Kishi. Any other names are fanon.

I'd also like to point out that Kishi literally wrote the plot for Road to Ninja. He had the same involvement he had in The Last. Road to Ninja isn't canon. The Last is. Even if Kishi wrote the novels himself, unless he declares it to be part of the manga continuity like he did with The Last and Boruto, they're non-canon.