(a) Annual actuarial valuation of mass-withdrawal-terminated plans. The valuation dates for the annual actuarial valuation required under section 4281(b) of ERISA are the last day of the plan year in which the plan terminates and the last day of each plan year thereafter for which an actuarial valuation is required to be performed under § 4041A.24 of this chapter.

(b) Valuations related to mass withdrawal reallocation liability. The valuation date for determining the value of unfunded vested benefits (for purposes of allocation) under section 4219(c)(1)(D) of ERISA is—

(1) If the plan terminates by mass withdrawal, the last day of the plan year in which the plan terminates; or

(2) If substantially all the employers withdraw from the plan pursuant to an agreement or arrangement to withdraw from the plan, the last day of the plan year as of which substantially all employers have withdrawn from the plan pursuant to the agreement or arrangement.