This is the ValueSet that contains all the codes in FDA National Drug Code (NDC) (http://hl7.org/fhir/us/davinci-pdex/ValueSet/FDANationalDrugCode) and FDA National Drug Code (NDC) (http://hl7.org/fhir/us/davinci-pdex/ValueSet/FDANationalDrugCode). E.g. what you have to deal with if you get resources containing codes in either of them