Question about "deleted" users and " non-activatied" users

For testing, I deleted some users from Network Admin>Users, and then tried to register the same username with the same email address back to WPMU. I got a message saying, username/email has been used. Then I checked wp_signup database table, and the user/email is still there even I deleted them from the dashboard. Why is that? How to get around that? (to allow deleted user/email to sign up again?) I assume I have to delete the wp_signup record to allow the same user/email to register again, right? (but people may not be confortable dealing with deleting directly from the database…:wink:

Another related question, if someone register a new username/email, and did NOT click the activation link sent to the email to activate the account (for instance, the email went to junk mail and got deleted by accident), and then he tries to register again, WordPress would say wait 2 days and try again. Will WordPress automatically delete the non-activatied account after 2 days? How does this “2-day” thing work in the backend?

Thank you for reading my questions. Hopefully I can know more about WP.