This information applies to AT&T, Bellsouth, and Yahoo addresses only. AT&T and Bellsouth are in cahoots with Yahoo. Yahoo “hosts” the email for AT&T and Bellsouth. That’s why you have to go to a Yahoo web page to check your email.
Account recovery information used to mean “security questions” such as your mother’s maiden name, first-grade teacher or favorite pet. After Yahoo got hacked a couple of years ago, they stopped using those question because the hackers had access to the answers. Now you have to use a separate recovery email address (such as a spouse’s or close friend) and a mobile phone number.
I know, I hate giving up my mobile phone number to anyone but this is a requirement if you want to stay safe.
If you had a merged email account, your emails, folders, and contacts are likely not deleted or missing. When your accounts were separated, that info remained with your Yahoo email account and is now located in your Yahoo inbox.