"The 2015 revised form and filing procedures would require 'after-the-fact' reporting of certain risk transfers through lump-sum windows and annuity purchases. The rationale provided by the PBGC is there is currently no available comprehensive, detailed and reliable source for information on risk transfers over a three-year period.... [T]he information requested by the new form applies to more than a single premium year, and ... reasonable estimates may be reported instead of exact counts. The instructions also include clarifying information regarding a new lump-sum window definition."