In context of https://jira.hl7.org/browse/FHIR-28375 we propose that the attribute definition be reverted back to the underlying FHIR R4 definition and that this attribute not be marked as Must Support.

We note that the definition of DiagnosticReport.effective[x] substantially changed compared to the FHIR R4 base definition.  We believe this to be an error which has led to attempting to use this attribute for a purpose that is already supported by .issued.  

As the field effectively represents the earliest and latest date of content referenced within DiagnosticReport that is should not be Must Support as that information can be fully derived from its content.

As the FHIR US Core profile is used for accessing and exchanging data based on what the source system has, this should not require the data source system to add functionality to enable Period as part of DiagnosticReport.effective[x].  Additionally, C-CDA does not impose this requirement either.