; and (2) the partially reinstated surcharge reinstated pursuant to paragraph (1) shall be considered a part of the rate base for purposes of determining the percentage changes in rates when the Postal Service files a notice of rate adjustment. (b) Subsequent rate increases The reinstatement described under subsection (a)(1) may not affect the calculation of the Postal Service’s maximum rate adjustment authority under subpart C of part 3010 of title 39, Code of Federal Regulations (or any successor regulation), for purposes of any rate increase that occurs following such reinstatement. (c) Commission review of system for regulating rates and classes for market-dominant products (1) Definitions In this subsection— (A) the term initial rate regulation review means the proceeding conducted under the order of the Commission entitled, Statutory Review of the System for Regulating Market Dominant Rates and Classifications (81 Fed. Reg. 9507 (December 20, 2016)); and (B) the term underwater product means a market-dominant class, product, or type of mail service that does not bear the direct and indirect costs attributable to that class, product, or type of mail service under current costing procedures. (2) Underwater products study Not later than 120 days after the date of enactment of this Act, the Commission, without delaying completion of the initial rate regulation review, shall begin a study, in conjunction with the Inspector General of the Postal Service and including notice and opportunity for public comment, to— (A) determine whether and to what extent any market-dominant classes, products, or types of mail service are underwater products; (B) quantify the impact of any operational decisions of the Postal Service on the direct and indirect costs attributable to any underwater products identified under subparagraph (A)