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To turn on delta processing on an existing or new Issuer Relationship Builder event:
Set the Store Last Run Time to Yes.
Check the Only process issuer relationships with changes since last run box.
Once both these values are set, each time the Issuer Relationship Builder event is run, it will check the update date on the issuer relationship record and compare it to the last build time for the relationship. If the update date is more recent, the relationship will be rebuilt. This prevents unnecessary processing of relationships that have not changed since last load.