we do not foreclose the possibility that under some circumstances an agency’s shifting of the policy goalpost (e.g., the evidentiary requirements for satisfying a particular statutory or regulatory standard) may lead us to conclude that the agency has acted arbitrarily or capriciously. See Smiley v. Citibank (South Dakota), N.A., 517 U.S. 735, 742, 116 S.Ct. 1730, 135 L.Ed.2d 25 (1996) (noting that “[s]udden and unexplained change [in an agency’s position], or change that does not take account of legitimate reliance on prior interpretation, may be arbitrary, capricious [or] an abuse of discretion” (alteration in original) (citations omitted) (quoting 5 U.S.C. § 706(2)(A)) (internal quotation marks omitted)); Hatch v. Fed. Energy Regulatory Comm’n, 654 F.2d 825, 834-35 (D.C.Cir.1981) (<HOLDING>); Pub. Serv. Co. of Ind., Inc. v. Fed. Energy
recognizing that production of a written insurance policy was unnecessary to prove the existence of the policy because the proof required was proof of the fact of insurance and not of the contents of a writing holding that an agencys sudden shift in the nature of proof required of the regulated party was not sufficiently explained and necessitated remand holding that an agencys sudden unexplained shift in the kind of data that a regulated party was required to submit was arbitrary holding that proof of an explicit agreement is not required holding that expert proof was not required for an asserted claim of ordinary negligence