The serial number should be on the outer most “layer” of packaging down to the unit of sale. This will typically be the carton or, in instances where no carton is deployed, the primary label. It would typically not be necessary to serialize both.

Please note this is different than a serial code on the corrugate shipper that may be deployed as a parent/child relationship to the individual units contained within the shipper. In this instance, the units (the children) each contain a unique serial code and the shipper (the parent) contains a separate code that links to the unit level codes in a database.

Serialization redundancy, without benefit of aggregation, adds cost and another layer of data management complexity that may not necessarily yield any additional security or supply chain benefits.