My default WP config is that users can’t register via wp-login.php. I’m using Theme My Login to handle registration.
If I turn on enforce unique nickname and users can’t register, the Admin must create new user and is required to provide First and Last names. Nickname is then created as first name + last name.
If username and nickname are not unique (i.e. both are jane doe), then on 1st login, user is required to change nickname.