It all depends if the data provider that you are using charges clay or not.
In this email example, this sounds like the data providers are giving you catch all emails that can't be validated and that's why the waterfall keeps running. They are putting a fix to this but in the meantime, I'd just use Prospeo and Findymail and if you can't find the email between the two of them, I'd move on and not worry about it. This way you don't lose credits running the whole waterfall which is usually unnecessary.