Comment:

In particular for resources with overlapping scope (and therefore potential for duplicate representation of the same content across queries for different resoruces), provide a unique source instance identifier that can be used to de-duplicate the data. E.g., for medications, we may need to check MedicationStatement to capture patient-reported meds, and MedicationRequest to capture the dispense quantity for prescriptions. But the same prescription could show up in both MedicationStatement and MedicationRequest, even though there is only one instance of that data in the source EHR. Require, or at least note using SHOULD language, that source EHR data instance identifiers are provided so that de-duplication of data can be conducted.

Summary:

Provide source EHR instance identifiers to allow de-duplication when the same EHR data is used to provide data across multiple FHIR resources with overlapping scope.