What specific document on the IRS website would that be? If a corrected form, such as a W-2 or 1099-MISC is issued, and if the change results in a change of the givers and/or recipient's tax liability, then an amended return is required - especially if the correction means you owe more to the IRS.
Generally, if you are issuing a corrected form for a prior year (2014 or earlier in this case) then the issuer is subject to fines and penalties for not getting it right by the original filing deadline. The fines and penalties isn't always true though, as it just depends on the specific situation.
For the purposes of this specific thread though, it would probably be most cost effective to treat the payback of the overpayment as a 2016 transaction so that no corrected forms have to be generated and submitted at all. But only the original poster can determine what is best for their specific tax situation.
