[Starson17]

Originally Posted by kovidgoyal

Just to clarify: calibre uses a custom field in EPUB files for the calibre date.

Thanks. I can see my answer above was incorrect. For reasons I won't go into, when I checked a saved EPUB before answering, there was no custom field for Calibre's date, so I incorrectly assumed it was the non-custom date field.

Here is the content of a Saved to Disk .opf file:

        <dc:date>1986-12-31T05:00:00+00:00</dc:date>
        <meta content="2009-12-30T05:00:00+00:00" name="calibre:timestamp"/>

The first is the non-custom date field ("Published" in Calibre) and the second is the custom date field ("Date" in Calibre).

The content.opf file inside an EPUB is essentially the same.