When an admin adds a user to a wordpress site, it does not actually create the user record, instead it reserves the email address and username *SOMEWHERE* until the user actually finishes the process and sets their password. This is problematic because if the user doesn’t finish the process, you now have orphaned data, and an email address that cannot be used to create an account again.
HOW can I delete these records?
Are you using a plugin for membership? Because WP doesn’t work the way you described – there is no “sign up process completion”.
“*now have orphaned data, and an email address that cannot be used to create an account again.*” – because their account has been created. So obviosuly they can’t create a new one with the same login details.
All user data is found under Users, unlkess you’re using a membership plugin. If so, then contact the membership plugin developer.