The Commissioner of Social Security shall recompute the primary insurance amounts applicable to beneficiaries whose benefits are based on a primary insurance amount which was computed under subsection (a)(3) effective prior to January 1979, or would have been so computed if the dollar amount specified therein were $11.50. Such recomputation shall be effective January 1979, and shall include the effect of the increase in the dollar amount provided by subsection (a)(1)(C)(i). Such primary insurance amount shall be deemed to be provided under such section for purposes of subsection (i).