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

Code	Display	Definition
OD	Order/EHR	Use “OD” for diagnoses entered into the EHR that are associated with an Order. Use “OD” for any diagnosis associated with an encounter that is entered into the EHR by a provider.
BI	Billing	Billing pertains to internal healthcare processes and data sources.
CL	Claim	Claim pertains to data from the bill fulfillment, generally data sources held by insurers and other health plans.
DR	Derived	Use “DR” for all diagnoses that are derived or imputed through analytical procedures (e.g., natural language processing).
NI	No information	Source of the diagnosis information is No information.
UN	Unknown	Source of the diagnosis information is Unknown.
OT	Other	Source of the diagnosis information is Other.