29 CFR 4231.11: Actuarial calculations and assumptions.

(a) Most recent valuation. All calculations required by this part must be based on the most recent actuarial valuation as of the date of filing the notice, updated to show any material changes.

(b) Assumptions. All calculations required by this part must be performed by an enrolled actuary based on methods and assumptions each of which is reasonable (taking into account the experience of the plan and reasonable expectations), and which, in combination, offer the actuary's best estimate of anticipated experience under the plan.

(c) Updated calculations. PBGC may require updated calculations and representations based on the actual effective date of a merger or transfer if that date is more than one year after the notice is filed, based on revised actuarial assumptions, or based on other good cause.