Can standard mail be used to return pt’s controlled meds brought from home but not returned when discharged?

I’m a pharmacist updating a policy on the handling/storage/returning of patients’ home medications if brought into the hospital when admitted. The pharmacy is responsible for handling and storing home medications and returning the medications when discharged. If the medications are inadvertently not returned they are sent through standard mail to the patient. Is it legal to send a patient’s controlled medication through standard mail? I’m finding a very grey area here. According to USPS: “For prescription medicines containing mailable narcotic drugs (controlled substances), only a pharmacist or medical practitioner, etc., who dispenses the medicine may mail such substances to the patients under their care.” If the controlled medications were not originally dispensed by the hospital pharmacy can the hospital mail them?