is entitled to monthly insurance benefits under this subchapter, (ii) is entitled to an annuity under the Railroad Retirement Act of 1974 [ 45 U.S.C. 231 et seq.], or (iii) would be entitled to a monthly insurance benefit under this subchapter if medicare qualified government employment (as defined in section 410(p) of this title ) were included within the meaning of the term “employment” for purposes of this subchapter; or