In the event an employer withdraws from the plan that was partitioned within ten years following the date of the partition order, withdrawal liability shall be computed under
section 1381 of this title with respect to both the plan that was partitioned and the plan created by the partition order. If the withdrawal occurs more than ten years after the date of the partition order, withdrawal liability shall be computed under
section 1381 of this title only with respect to the plan that was partitioned (and not with respect to the plan created by the partition order).