User blog comment:Gufuawa12/A question I have to ask/@comment-11494103-20130813200055

Once an account is assigned to an email or game center ID, it will never get deleted. As for anonymous accounts, you can open a third account through the anonymous option (it has no effect on any accounts you already possess and it will cause their deletion), but there is no guarantee the new anonymous account will be safe from deletion until the anonymous account is tied to an email. With that said, I have an anonymous account on each of my devices. I have deleted and reinstalled the app many times and have never lost the progress on my anonymous accounts (maybe they have been tied to my email somehow without my being aware). But if you make any progress at all on the anonymous account, I would strongly suggest you tie it to an email account to protect your progress on the anonymous account.