http://www.intertwingly.net/wiki/pie/PaceAllowDuplicateIDs

[Bob Wyman]

+1 with a comment:   If this Pace is accepted (and I hope it will be) the issue of Duplicate IDs should probably be dealt with in Mark’s Implementation Guide.[1]   Atom supports the publishing of "newer versions" of an entry which use the same atom:id as earlier versions of the same entry. It is not required that atom:updated be modified when a newer version is written. If the PaceAllowDuplicateIDs is accepted, it will be permitted to have multiple entries with the same atom:id in a single feed. However, the Pace language says processors “SHOULD” regard as feed generation errors any entries which duplicate both the atom:id and atom:updated of another entry in the same feed. Thus, feed authors who wish to publish feeds with duplicate atom:ids should ensure that any entry which duplicates an entry already in the feed has a different value for atom:updated. This constraint is not a requirement of the language, but it is a clear derivative of it. Basically, you don’t have to update atom:updated unless you think it makes sense OR you are publishing to a feed that already has an entry with the same atom:id as the atom:id of the entry you are currently publishing.         bob wyman   [1] http://diveintomark.org/rfc/draft-ietf-atompub-impl-guide-00.html