<prompt> Translate the following text to EnglishTume ilieleza kwamba kutokubaliana kwake na wazo la viwango vya mkataba kulitegemea kutokuwa na uhakika mkubwa kuhusu upendeleo wa kisheria wa kuchunguza viwango vilivyokubaliwa baada ya tukio, badala ya katika ukaguzi wa awali.  <response>: The Commission explained that its reluctance to pursue the concept of contract rates was based on substantial uncertainty regarding the legal sufficiency of examining agreed-upon rates after the fact, rather than in a prior review. 