Do you have Duplicate Hardware IDs?
https://support.symantec.com/en_US/article.TECH163349.html
If you are running SEP 14 RU1 MP1 you can add the settings to the conf.properties on each of your SEPMs.
Wait a few days and the counts should get closer.
From the same document you can run the tool SEPM Repair tool on each of your SEPMs to identify the clients with this duplicate Hardware ID issue.
Thanks,
John