I do not practice in NC so I can only provide general information. Every state has a medical records retention law. You need to look at the law and see how it defines medical information. If billing info is considered medical info, then the physicians should probably retain the eobs just to be safe.
On the other hand, healthcare providers could take the position that eobs are not part of the medical or billing record because they are created by a third party payor.
Finally, healthcare providers may also want to review their contracts with third party payors to see if they require an additional retention.