Whether the "as of" language in 29 U.S.C. § 1391 sets the measurement date as the deadline by which actuaries must select the assumptions that underlie the withdrawal-liability calculation. The Court must determine if actuarial assumptions are factual inputs that must be frozen on the measurement date or tools that can be selected later. This involves interpreting the relationship between 29 U.S.C. § 1391 and 29 U.S.C. § 1393.

• The "as of" language in 29 U.S.C. § 1391 requires that actuarial assumptions be "frozen" on the measurement date, meaning the actuary must use assumptions that were "in effect" on that date.
• Actuarial assumptions are factual inputs into the unfunded vested benefits (UVB) calculation, similar to hard data such as the number of plan beneficiaries.
• ERISA contains a broad antiretroactivity principle, as evidenced by 29 U.S.C. § 1394, which prohibits applying new "plan rules or amendments" adopted after an employer withdraws.
• Allowing plans to adopt assumptions after the measurement date invites manipulation, enabling plans to retroactively select assumptions to increase the liability of withdrawing employers.

• The "as of" requirement in 29 U.S.C. § 1391 applies only to the hard data that feeds the UVB calculation, not to the tools used to perform the calculation.
• 29 U.S.C. § 1393 provides no textual deadline for the selection of actuarial assumptions.
• To comply with the requirement in 29 U.S.C. § 1393(a)(1) to provide the actuary's "best estimate of anticipated experience," actuaries must be able to rely on the most up-to-date data, which may not be available until after the measurement date.
• Actuarial assumptions are predictive judgments and tools, not observable facts that are "in effect" on a specific date.

• The Court held that withdrawal liability can be calculated based on actuarial assumptions adopted after the measurement date.
• Regarding 29 U.S.C. § 1391, the Court reasoned that "as of" is understood "to assign an event to one time and the recognition of it to another" (citing W. Follett, *Modern American Usage*), meaning hard data is fixed on the measurement date, but the calculation can occur later.
• The Court distinguished between "facts" and "tools," concluding that actuarial assumptions are "predictive judgments" and tools used to calculate UVBs rather than observable factual inputs.
• The Court found that 29 U.S.C. § 1393 contains no deadline for selecting assumptions, and it declined to read limitations into the statute that do not appear in the text (citing *Romag Fasteners, Inc. v. Fossil Group, Inc.*).
• Applying the principle from *Russello v. United States*, the Court noted that because Congress included a deadline for assumptions in 29 U.S.C. § 1399(c)(1)(A)(ii) but omitted one in 29 U.S.C. § 1393, the omission was likely intentional.
• The Court reasoned that the mandate in 29 U.S.C. § 1393(a)(1) for the actuary's "best estimate" supports post-measurement date selection, as requiring stale data would prevent actuaries from using the most current information.
• The Court rejected the antiretroactivity argument, noting that the limits in 29 U.S.C. § 1394 apply to "plan rules or amendments," which the parties concede do not include actuarial assumptions.
• The Court concluded that "policy concerns cannot trump the best interpretation of the statutory text" (citing *Patel v. Garland*), and that any manipulation of assumptions can be addressed through the arbitration process provided in 29 U.S.C. § 1401(a)(3)(B)(i).