Duplicate inventory report

I have a powershell scanner configured to pull some data on local user and device certificates from the certificate store in Windows. This is working great. The powershell scanner pulls three attributes - Subject, Expiration, Issuer for a specific certificate template from both the user and device personal certificate store. What I'd like to do now is create either a collection or report that tells me which devices have more than one certificate (of each type, user/device). So far, I've not been able to do this and I'm not sure that it's possible. Has anyone managed to create a report or collection that is populated by devices with duplicate inventory items?