About Identity and Handles
A person in NUU has two public names. One name is permanent. The other name can change. This split is the reason attribution stays stable when a username changes.
Permanent identity
Every public profile has a permanent identity. The service creates it when the public profile is created. It does not change later.
Other NUU products store this permanent identity when they name you. The public page also uses it. If your handle changes, the public page stays the same. Old links that used a handle still find you. They move to the permanent page.
When two identities merge in a claim, the ghost keeps its permanent identity. The old public profile, if you had one, is retired. Other products that stored the ghost identity keep working. Products that stored the retired identity no longer find that page.
Handle
A handle is the short public name. It is the username from your NUU account. You claim that username on your NUU account. NUU Profiles copies it onto your public profile.
You cannot edit the handle in NUU Profiles. If you change the username on your NUU account, the handle on your public profile updates after a short wait.
A public profile can exist with no handle. That happens when your NUU account has no username yet, or when that username is not free. The permanent identity is then the only public identifier.
A live ghost usually has no handle. A ghost is not tied to an account, so it has no username to copy.
What happens when a handle changes
When a handle changes, the old handle is retired. No other public profile can use a retired handle. This keeps old names from pointing at a new person.
The new handle must be free. If another public profile already holds it, or if it is retired, your public profile keeps its current handle.
Why this shape exists
Usernames are easy to say and easy to type. They are also easy to change. If other products stored only the handle, every rename would break attribution.
The permanent identity is hard to say. It is stable. Other products can show the current handle and still point at the same person.
This is the same idea as a person who changes a nickname. Friends still know who they are. The legal identity did not change.
For how other products show this record, see About Attribution. For the full noun set, see Core Ideas.