The Versions page states the following:

"There is no explicit version marker in the content of FHIR resource instances. Instead, the version supported by a given system is declared using the conformance framework. The resources CapabilityStatement and StructureDefinition have properties for declaring the FHIR specification version, and these may be used to determine which version of FHIR an implementation is using to aid in validation and integration."

We recommend that FHIR provide a mechanism to allow instances to carry version information. For example in a CDS prefetch capability, the information is pushed to the service and the service may not know what version of FHIR is being sent to it. It is not uncommon for systems to process FHIR instances without knowledge of the endpoint from where these instances originated nor any information about the profile against which these instances conform. Without knowing the version