I have a pharmacy claim that I want to map to the DRUG_EXPOSURE table. The claim contains an NDC code, but no explicit route or unit field. Route and unit can be found in an NDC look-up table. Do I need to (or should I) store anything in route_source_value and dose_unit_source_value? Or, should I just populate route_concept_id using an NDC-to-route look-up table and leave the source-related variables null?