We have a feature called rename detection that can be found under configuration/server options. By default, it is enabled; however, we have added a new setting to this feature that will only check on the model and serial number and not the MAC address; this could help alleviate the duplicate issue you are experiencing.
If you cannot collect the correct details from agentless scanning, then a good recommendation would be to use the LsAgent. This way, you capture information daily without the challenge of trying to capture it when clients are on the VPN.
