For purposes of this subsection, wages (determined as provided in paragraph (5)(C)) which, according to reports received by the Commissioner of Social Security, are paid to an individual during a taxable year shall be presumed to have been paid to him for services performed in such year until it is shown to the satisfaction of the Commissioner of Social Security that they were paid for services performed in another taxable year. If such reports with respect to an individual show his wages for a calendar year, such individual’s taxable year shall be presumed to be a calendar year for purposes of this subsection until it is shown to the satisfaction of the Commissioner of Social Security that his taxable year is not a calendar year.