The notion of 'unknown' doesn't really make sense here.  Either you know the issue is "entered-in-error" or you presume it's accurate (or at least as accurate as any other usage statement).  Also, "completed" is going to be confusing to a lot of people as they'll presume it means the same thing it meant in MedicationStatement - and it doesn't.  Suggest renaming 'completed' to 'recorded'.  Also, Grahame raised the question of whether the notion of 'draft' is relevant or not.

See discussion here: https://chat.fhir.org/#narrow/stream/179249-Medication/topic/MedicationUsage.2Estatus