Problem being that when an account is Deleted, the IP and email address can be added to the “Screened” lists.
Member names of deleted accounts can be re-used.
It might help if you consider context when thinking of the definition of “Identity”
To me
Email Address - identifies the person in the “real world” i.e. verification that the person using that email address is that person
Member Name - Identifies the person to other forum members
Member Id - Used in the code to identify the member’s account