Currently when you export from Advance Steel to Naviswork via the NWCOUT exporter the AS Properties don't transfer over. If you append the native dwg into Naviswork the AS properties don't transfer.
If you export to Navisworks via dwfx the AS properties do transfer over however each time this is exported it give the AS elements a new GUID. This GUID is what is used to append additional data to the elements as well as managing clash detection.
I would suggest that the NWCOUT exporter should include the AS properties and the GUID is retained throughout the project.