This is the ValueSet that contains all the codes in Immunization Recommendation Date Criterion Codes (http://hl7.org/fhir/ValueSet/immunization-recommendation-date-criterion) and Immunization Recommendation Date Criterion Codes (http://hl7.org/fhir/ValueSet/immunization-recommendation-date-criterion). E.g. what you have to deal with if you get resources containing codes in either of them