If identity is a concern, maintain a list of old usernames. But in the real world, there are always extenuating circumstances in which allowing a username to ch

If identity is a concern, maintain a list of old usernames. But in the real world, there are always extenuating circumstances in which allowing a username to change is good policy. Admins could blindly enforce a "never change usernames" policy, but why not just use a meaningless key and avoid the risk?