Systems and methods for synchronization including the use of a global equivalency identification datum or set of datum. A universally unique identification datum may be associated with each independently created associated data set. In some embodiments, a synchronization server software element may be responsible for maintaining synchronization for a plurality of clients, including software elements or devices. A record believed to be new by the software elements may verify that the record is actually new. In some embodiments, verification of the record's newness involves assuming that the local ID is a global identification datum and comparing that datum to the all the sets of datum that the Sync-Server knows about. The synchronization server software element may use a table to hold information for all of the records known to that element. In some embodiments these records may have been deleted in the past.