If you feel this article consume much resource.
How to repair duplicate IDs on cloned Symantec Endpoint Protection 12.1 clients
http://www.symantec.com/docs/TECH163349
Then go with this step.
Change the Removal of clients after 30 days to 1 day.
So the duplicate entries will be deleted & removed from SEPM and if any client not a duplicate entry is deleted from SEPM because of this settings.
Dont worry about that automatically when the clients online it will be back to the SEPM and register itself.