[AlanHK]

I start most of my epubs by copying an existing file and then replacing text, images, etc, especially when they're in a series.

So I started with "Old Title" (an epub2) and was making "New Title".
Imported new text and images then did a TOC, then edited the metadata.

All looked fine. Searched for "Old Title" in the html and the OPF; no mentions left.

I went to ePub3-itizer to make a file for iBooks. It wanted to save the file as "Old Title-epub3.epub". Of course I could rename it, but I wondered where the hell it was getting that name from.

The OPF:
<dc:title>New Title</dc:title>

I used Sigil's tool Metadata editor, changed the title (which as expected, changed the above line in OPF); still ePub3-itizer thought it was "Old Title".

Of course, there was one file I hadn't looked in: the NCX. And there it was:

<docTitle>
<text>Old Title</text>
</docTitle>

So:
1) Why is this here at all? What uses this, aside from ePub3-itizer?
2) Why doesn't the Metadata editor update <docTitle> as well as the OPF <dc:title>?
And/or show there is a discrepancy?

Neither the "Well-Formed Check" nor Epubcheck raises a flag at them mismatching

I found that if I used Tool/Generate TOC, the title was updated in the NCX to match the OPF. But also of course it would make a completely new TOC, and I'd lose any manual edits. But I would not even have known it was necessary if ePub3-itizer hadn't brought it to my attention, since I always use the TOC editor rather than the code directly.