42 CFR §489.40

1. (a)As used in this subpart, “incorrect collections” means any amounts collected from a beneficiary (or someone on his or her behalf) that are not authorized under subpart C of this part.
2. (b)A payment properly made to a provider by an individual not considered entitled to Medicare benefits will be deemed to be an “incorrect collection” when the individual is found to be retroactively entitled to benefits.