[DNSB]

Originally Posted by jackie_w

I don't believe there's any need to do that for calibre users. The calibre TOC Editor automatically keeps the NCX and NAV files correct and in sync in epub3 books.

Pretty much the same for those who use Sigil. The nasty bit is that this assumes that TOC entries are done use using header tags and not generated manually. Sadly manual TOCs are too common and often have weird errors in them. As in one recent ebook, where the nav.xhtml and toc.ncx were both present and both were incorrect and out of step with each other. This particular ebook also had the content split at random spots so it was easier to merge the whole futtering mess into one file and resplit it at chapter boundaries.