This element is found at this location (XPath):

The year of public release of data online should be listed as the <pubDate> element. Because this element may be used in constructing citations, the pubDate also should reflect the ‘recentness’ of a package, with pubDate updated along with significant revision or data additions (e.g., corrected data, or additions to an ongoing time series). There is an argument for pubDate referring to original date of release, but this is probably only useful for static data packages, or if the only metadata changes are to enhance discovery.