One of my email addresses is {MyNameKP}@gmail.com. “KP” were just random letters I picked years ago and they don’t mean anything. I also own {MyName}@hotmail.com. Someone once asked why I don’t use {MyName}@gmail.com, so I went home to try to sign up for it, but Gmail said the address already exists. I figured someone else had it and might sell, so I emailed them. Gmail auto-replied that the address doesn’t exist. Why can’t I register an address that isn’t there? Who knows ¯\_(ツ)_/¯

Aren't email addresses reserved once you delete an account? Maybe that's what happened?