You must expose the document version to an API entry point in order to expose the document types to the API Services. For example, you can expose the ISPFDesignDocumentVersion by relating the interface definition or class definition to the SPFAPIEntryPoint instance. All valid relationships appear as if they belong to the document version for the exposed document types.
If a relationship definition ends with the ISPFDocumentVersion interface definition and there is more than one exposed class definition that realizes the ISPFDocumentVersion interface definition, it is possible that the correct end object cannot be determined. This is because there are two or more class definitions available for the end of the relationship. When this occurs, a warning message is written to the Metadata tracing category in the trace file to record the reason why the navigation in that direction cannot be included. You can bypass this behavior by exposing the specific interface definition that the relationship definition specifies for that end.
If you use an Edge Definition, you can specify the ValidEndInterfaceDefUIDs property on the Edge Definition so that the metadata generation code can locate which types are potential targets for the navigation. In that case, if the existing two class definitions and the ISPFDocumentVersion interface definition are all exposed, the navigation goes to ISPFDocumentVersion and not to the two class definitions.