For errors found in published ebooks it is generally recommended that corrections be sent to support@j-Novel.club There are various reasons for that but it basically comes down to it will get seen and addressed faster. It is also important to note that corrections found in the final QC before an ebook is published won’t always be applied to prepub parts on the website, so if the book has been published and you find an error while reading the prepub parts on the site it probably was already caught.

Something like this was brought up long ago https://forums.j-novel.club/topic/243/grimgar-of-fantasy-and-ash-printed-version/11 To summarize, those types of content are produced by the anime production committee and would require a whole separate license, and that license would have to be from a company that JNC has virtually no ties with, so more then likely it will not be happening.

@drewjn I'm the same way about checking, though I dunno if it's as consistent as "every year or two." I remember really liking the manga though, and wanting to see the source material. It's a series that even now sticks out in my brain, for better or for worse (as far as some of the anime antics are concerned).