Not always it is supported or intended to start right away with a AutoNumber for CAD Docs. There are cases for import or special features in CAD especially when autonumbering is configured with manual overwrite. It would be great to have a renumber feature for INWORK objects which might be already checked in but did not get released yet - initial revision.
After a revise this feature should not be available for that object anymore.
Best practice s to use for wtparts same sequence as for CAD Models, CAD Drawings should get there own sequence