Did you know Google identifies Google Merchant Center accounts by the email address used to log in?

Yes. Google identifies your Google Merchant Center account with the email address used to log in and an "account number". If you ever log in to your Googlebase account using a different email, you might have two Googlebase accounts and not even know it. You can only verify and claim one URL per account so if you have already claimed your URL per Google's new requirement and suddenly the URL is unclaimed, you'll definitely want to check and make sure you're logging in to your account with the proper email address.