http://hl7.org/fhir/StructureDefinition/valueset-expirationDate|5.2.0

The date when the value set version is no longer expected to be used to create new content. This is the first date-time when the value set version becomes Inactive, so this value SHALL present on all Inactive value set versions. The start Date_time is expected to be as of 0001 UTC of the Expiration Date.