Dates and time... Dates and time are painful, dates and time are complex, "dates and time are the most complex objects we use on a daily basis" used to say Reuters' Misha Wolf in the HTML WG in the good ol'days.

Excerpt from section 2.2.7 of OPF 2.01:

The date element has one optional OPF event attribute. The set of values for event are not defined by this specification; possible values may include: creation, publication, and modification.

Excerpt from section 3.4.6 of EPUB Publications 3.0:

The date element must only be used to define the publication date of the EPUB Publication.
...
Only one date element is allowed.

Ahem... So EPUB3 allows only two dates for a package: the publication date and the last-modification date (through a <meta property="dcterms:modified"> element). It's impossible to preserve the date of creation or various modification dates. Is it only me or this change from EPUB2 to EPUB3 is weird?

Please note that to insert a publication date into an OPF document ready for distribution, you must modify it and rezip the whole package. So if an OPF document does have a <dc:date> publication element, its content value must be equal to the last-modified date!!! In other terms, this is totally useless. Wow.