; and (II) for any calendar year after 2018, the annual dollar amount for 2018 multiplied by the ratio of— (aa) the national average wage index (as defined in section 209(k)(1)) for the second calendar year preceding the calendar year for which the determination is made, to (bb) the national average wage index (as so defined) for 2016. (iv) For purposes of this subparagraph— (I) the term year of work means, with respect to an individual, a year to which 4 quarters of coverage have been credited based on such individual’s wages and self-employment income