This is purely a UI limitation, because this information is actually returned to the site via the JNC API. In fact, the API response contains both the publishing date of the volume itself, plus the individual publishing dates for each eBook type (amazon/kobo/ibook/etc).
For example, if we look at For My Daughter volume 3, the API response lists a publishing date of "2017-10-24T15:00:00.000Z" for the volume itself, and "2017-10-25T07:00:00.000Z" for the ebook sellers.
There are also created/published/expiration dates for all individual parts in the volume, as well as the date that the volume's entry was created... plus lots of other dates for things.