This is the ValueSet that contains all the codes in ValueSet - Tracking Number Type (http://hl7.org/fhir/us/mdi/ValueSet/ValueSet-tracking-number-type) and Tracking Number Type (http://hl7.org/fhir/us/mdi/ValueSet/vs-tracking-number-type). E.g. what you have to deal with if you get resources containing codes in either of them