A recipient that made an unallowable expenditure or otherwise failed to discharge its obligation to account properly for funds shall return an amount that—

(a) Meets the standards for proportionality in § 81.32;

(b) In the case of a State or local educational agency, excludes any amount attributable to mitigating circumstances under the standards in § 81.23; and

(c) Excludes any amount expended in a manner not authorized by law more than five years before the recipient received the notice of a disallowance decision under § 81.34.