We will add language indicating that the various references in Coverage SHOULD be handled using Reference.reference (and possibly Reference.display) if the target resource is available from a RESTful endpoint or using Reference.identifier and Reference.display if the resource is not available on a RESTful endpoint.  A relative reference to a contained resource is generally not appropriate if an identifier for the target is known. Will update the example instances in the IG to align with this principle and to show both mechanisms of reference.