(a) The legal regulated rent for any vacancy lease entered into after June 15, 1997 shall be as hereinafter provided in this subdivision. The previous legal regulated rent for such housing accommodation shall be increased by the following:
(1) if the vacancy lease is for a term of two years, 20 percent of the previous legal regulated rent; or
(2) if the vacancy lease is for a term of one year, the increase shall be 20 percent of the previous legal regulated rent less an amount equal to the difference between:
(i) the two year renewal lease guideline promulgated by the rent guidelines board applied to the previous legal regulated rent; and
(ii) the one year renewal lease guideline promulgated by the rent guidelines board applied to the previous legal regulated rent. In addition, if the legal regulated rent was not increased with respect to such housing accommodation by a permanent vacancy allowance within eight years prior to a vacancy lease executed on or after June 15, 1997, the legal regulated rent may be further increased by an amount equal to the product resulting from multiplying such previous legal regulated rent by six tenths of one percent and further multiplying the amount of rent increase resulting therefrom by the greater of:
(a) the number of years since the imposition of the last permanent vacancy allowance; or