If the <patient_id> source and value are already mapped to a PATIENT_NUM, then the update date should be compared to the existing record's update date. If the new record has a more recent date, then update the current patient record with this data.
Example:
<patient update_date ="2006-05-0418:13:51.00">
<patient_map_id source="MGH">123</patient_map_id>
</patient>
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