I have seen a few edits that clearly are being done by the post owner but for some reason the post owner has two accounts with the same user name. The system should at least tell the person how to get the accounts merged.
The problem here is that the user name is not unique.
So how would you tell that
You could have a process that looks at IP addresses shared by the accounts, or even shared e-mail addresses etc, but the IP check could fail if you have many users coming from the same place - e.g. a college or large company.
It's probably easier to let humans spot things like this - we're far better at pattern recognition than computers.