How prevalent are duplicate email accounts?

Apple has sold over 800 million iPhones worldwide, each with a AppleId email account.  Apple requires the AppleId email account be linked to a non Apple email server for email storage.    These non Apple email servers are used to establish credit and debit accounts with MasterCard and Visa in the USA.  Other similar transaction companies are used in the United Kingdom and other countries.   Each account on MasterCard and Visa must be linked to a bank account for money transfer upon a user's purchase from a merchant.   Now all of these contacts are linked together individually and securely for  each owner of the email address.
However, there is one small problem.  With 800 million AppleIdAccounts is it possible for a duplicated email address to be created and used?
The unfortunate answer is yes.
My wife shares a duplicate AppleId email address with a person in Scotland with the same name.   This duplicate is created when the persons name is attached to the  suffix  @icloud.com in the Applied email address.  Apparently every Apple account has an @icloud.com address created when the non Apple email server address is created.
The obvious solution is not to use your name when you create an Apple inked email address.  I used an acronym of our first and last names.  My wife used her proper name.  I guess most folks use their name when the non apple email server will permit it's use.

Howie