Union of http://hl7.org/fhir/sid/ndc and http://hl7.org/fhir/sid/ndc
This is the CodeSystem that contains all the codes in National drug codes (http://hl7.org/fhir/sid/ndc) and National drug codes (http://hl7.org/fhir/sid/ndc). E.g. what you have to deal with if you get resources containing codes in either of them