When a Plan Sponsor, after submitting its Reconciliation payment request, or its final payment request using the RDS Secure Website Reconciliation process, discovers that it agreed to incomplete (as opposed to inaccurate) retiree data and/or reported incomplete cost data (see "For purposes of the RDS Program, what is "inaccurate" data, as opposed to "incomplete" data?" for examples of what constitutes incomplete data), and has reason to believe that the incomplete data had the net effect of causing the Plan Sponsor to be paid (or that it will be paid) too little in subsidy for the application, it is not required to quantify that difference in subsidy. It is permissible to not disclose the corrected data or the subsidy discrepancy to CMS.
The Plan Sponsor, however, may choose to quantify the difference, and attempt to acquire the difference in subsidy by requesting a reopening. See "How would an RDS Plan Sponsor request a reopening of a reconciliation or final payment determination, when it believes the determination is incorrect due to inaccurate or incomplete cost data?" for information regarding how to request such a reopening.
After requesting a reopening, CMS will notify the Plan Sponsor whether it may acquire the difference in subsidy, and if so, what further steps the Plan Sponsor must take in order to do so.