This code system http://hl7.org/fhir/narrative-status defines the following codes:

CodeDisplayDefinition
generatedGeneratedThe contents of the narrative are entirely generated from the structured data in the content.
extensionsExtensionsThe contents of the narrative are entirely generated from the structured data in the content and some of the content is generated from extensions
additionalAdditionalThe contents of the narrative may contain additional information not found in the structured data. Note that there is no computable way to determine what the extra information is, other than by human inspection
emptyEmptyThe contents of the narrative are some equivalent of "No human-readable text provided in this case"