applicable part B drug of the manufacturer furnished after December 31, 2019, for which payment was made under this section or under a separate ambulatory classification group pursuant to section 1833(t) during the period. (B) Audits by manufacturer of information provided A manufacturer may, as determined by the Secretary, audit the information provided (or required to be provided) under subparagraph (A). (C) Audits by Secretary The Secretary may audit the information provided (or required to be provided) under subparagraph (A) and the determination of the billing-code level rebate amount, including the manufacturer-level billing-code level ASP and inflation-adjusted billing-code level ASP, under paragraph (4). (D) Adjustments based on audit results The Secretary shall make adjustments to rebates and average sales price as appropriate based on the results of an audit conducted under subparagraph (B) or (C). (4) Determination of billing-code level rebate amount (A) In general The amount of the rebate specified under this paragraph for a manufacturer for a rebate period, with respect to applicable part B drugs of a manufacturer assigned to a billing code, shall be equal to the product of— (i) the total number of units of such drugs of the manufacturer assigned to the billing code for which payment was made under this section or under a separate ambulatory classification group pursuant to section 1833(t) for the rebate period