"You aren't required to use the new mortality tables when preparing the year-end benefit obligation accrual; other available information may represent a better estimate of mortality for the population of participants in your plan. However, you are required under generally accepted accounting principles (GAAP) to use your best estimate when measuring the benefit obligation, and in making that estimate, to consider all available information through the issuance date. Your auditors will want you to provide them with documentation that the selected mortality assumptions result in the best estimate of expected mortality for plan participants based on conditions existing as of the measurement date."