This case-sensitive code system http://hl7.org/fhir/us/cdmh/CodeSystem/pcornet-diagnosis-classification-codes defines the following codes:

Code	Display	Definition
AD	Admitting	Classification of Diagnosis is Admitting.
DI	Discharge	Classification of Diagnosis is Discharge.
FI	Final	Classification of Diagnosis is Final, Ambulatory encounters would generally be expected to have a source of “Final”.
IN	Interim	Classification of Diagnosis is Interim, it is not necessary to populate interim diagnoses unless readily available.
NI	No information	Classification of Diagnosis has No information.
UN	Unknown	Classification of Diagnosis is Unknown.
OT	Other	Classification of Diagnosis is Other.