20 C.F.R. § 418.3678
If we become aware within 60 days of the date of our initial determination or our decision following a case review or telephone hearing, that a clerical error was made in determining whether or not you are eligible for a subsidy (either in whole or in part), we may issue a revised initial determination which would be effective back to the date you originally filed your application or the effective date of a subsidy changing event, provided you meet the requirements in § 418.3101 . We may revise an initial determination or decision regardless of whether such revised determination or decision is favorable or unfavorable to you. If the revised determination or decision (which is a new initial determination) is not favorable to you, you will not be responsible for paying back any subsidy received prior to the revised determination or decision. We will mail you a notice of the revised determination which will explain to you that we have made a revised determination and that this determination replaces an earlier determination, how this determination affects your subsidy eligibility, and your right to request a hearing.
20 C.F.R. §418.3678