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.