Duplicate scans of computers

I've noticed that for some reason, I've got multiple entries for the same workstation when I've done domain scans. Later we changed the system name of the computer (ie its name in active directory) and now we have duplicates. Is there any way to make the scans with the same service tag (which is the serial numbers in our case) to be a unique field, and whenever a scan is done that has the same serial number for it to override the info for that computer? We tend to do a lot of reformats and change of the computer's name on the domain, and it would be nice to simply get a new scan to update the computer with the new domain name and scanned info, rather than create a brand new entry.

Also, I'm not sure how many computers are duplicated, so it would be nice to create a report with the service tags and a count of how many that have the same info, but I have no clue how to do this. (Alternatively it could be just a listing of the duplicate entries rather than all the entries with a count of how many have the same service tag) Editing the default reports I couldn't seem to get a summary of the field, so I'm a bit lost.