42 CFR §424.522

1. (a)Reassignments.
   1. (1)The effective date of a reassignment of benefits under § 424.80 is the later of the dates identified in § 424.520(d)(1)(i) and (ii).
   2. (2)Retrospective billing in accordance with a reassignment of benefits and as described in § 424.521(a)(1) is permissible if the circumstances in § 424.521(a)(1) are applicable.
2. (b)Form CMS-855O enrollment. The effective date of a Form CMS-855O enrollment is the date on which the Medicare contractor received the Form CMS-855O application if all other requirements are met.