As-of-right floor area bonuses are not permitted in the Special Midtown District, except in accordance with 

Section 81-23        (Floor Area Bonus for Public Plazas).

Any floor area bonus granted by certification for through block gallerias prior to August 6, 1998, shall remain in effect provided, however, that such certification shall automatically lapse if substantial construction, in accordance with the plans for which such certification was granted, has not been completed within four years from the effective date of such certification.