(a) Plan benefits. A participant's or beneficiary's plan benefits are determined under the plan's provisions in effect on the plan's termination date. Notwithstanding the preceding sentence, an amendment that is adopted after the plan's termination date is taken into account with respect to a participant's or beneficiary's plan benefits to the extent the amendment—

(b) Residual assets. In a plan in which participants or beneficiaries will receive some or all of the plan's residual assets based on an allocation formula, the amount of the plan's residual assets and each participant's or beneficiary's share thereof is determined under the plan's provisions in effect on the plan's termination date. Notwithstanding the preceding sentence, an amendment adopted after the plan's termination date is taken into account with respect to a participant's or beneficiary's allocation of residual assets to the extent the amendment does not decrease the value of the participant's or beneficiary's allocation of residual assets under the plan's provisions in effect on the termination date.

(c) Permitted decreases. For purposes of this section, an amendment shall not be treated as decreasing the value of a participant's or beneficiary's plan benefits or allocation of residual assets to the extent—

(d) Distress terminations. In the case of a distress termination, a participant's or beneficiary's benefit liabilities are determined as of the termination date in the same manner as plan benefits under this section.