(a) Reduced benefits
If title II of the Social Security Act [42 U.S.C. 401 et seq.] is amended at any time after December 31, 1974, to reduce the eligibility requirements for old-age insurance benefits, disability insurance benefits, wife's insurance benefits payable to a wife, husband's insurance benefits, child's insurance benefits payable to a child of a deceased individual, widow's insurance benefits payable to a widow, widower's insurance benefits, mother's insurance benefits payable to a widow, or parent's insurance benefits, such reduced eligibility requirements shall be applicable, in accordance with regulations prescribed by the Board, to individuals, spouses, or survivors, as the case may be, under section 231a of this title to the extent that such reduced eligibility requirements would provide such individuals, spouses, or survivors with entitlement to annuities under such section 231a of this title to which they would not be entitled except for such reduced eligibility requirements: Provided, however, That no annuity shall be paid to any person pursuant to the provisions of this subsection if that person does not satisfy an eligibility requirement imposed by section 231a of this title of a kind not imposed by the Social Security Act [42 U.S.C. 301 et seq.] on December 31, 1974, or an eligibility requirement imposed by section 231a of this title of a kind which was imposed by the Social Security Act on December 31, 1974, but which was not reduced by the amendment to that Act: Provided further, That the annuity amounts to which such individuals, spouses, or survivors will be entitled under this subchapter by reason of the provisions of this subsection shall be only such amounts as are determined under the provisions of section 231b(a), 231c(a), or 231c(f), respectively, of this title.

(b) Additional eligible beneficiaries
If title II of the Social Security Act [42 U.S.C. 401 et seq.] is amended at any time after December 31, 1974, to provide monthly insurance benefits under that Act to a class of beneficiaries not entitled to such benefits thereunder prior to January 1, 1975, every person who is a member of such class of beneficiaries shall be entitled to annuities under section 231a of this title, in accordance with regulations prescribed by the Board, in an amount equal to the amount of the monthly insurance benefit to which such person would have been entitled under the Social Security Act [42 U.S.C. 301 et seq.] if service as an employee after December 31, 1936, had been included in the term "employment" as defined in that Act.

(c) Reduced conditions of entitlement; expanded benefits
If section 226 [42 U.S.C. 426] or title XVIII [42 U.S.C. 1395 et seq.] of the Social Security Act is amended at any time after December 31, 1974, to reduce the conditions of entitlement to, or to expand the nature of, the benefits payable thereunder, or if health care benefits in addition to, or in lieu of, the benefits payable under such section 226 or such title XVIII are provided by any provision of law which becomes effective at any time after December 31, 1974, such reductions in the conditions of entitlement to benefits, such expanded benefits, or such additional, or substituted, health care benefits shall be available to every employee (as defined in this subchapter), and those deriving from him, in the same manner, and to the same extent, as if his service as an employee after December 31, 1936, had been included in the term "employment" as defined in the Social Security Act [42 U.S.C. 301 et seq.]. The Board shall have the same authority, in accordance with regulations prescribed by it, to determine the rights of employees who will have completed ten years of service (or five or more years of service, all of which accrues after December 31, 1995), and of those deriving from such employees, to benefits provided by reason of the provisions of this subsection as the Secretary of Health and Human Services has with respect to individuals insured under the Social Security Act.

(d) Limitations
Notwithstanding the provisions of subsections (a), (b), and (c) of this section—

(1) No annuity or other benefit shall be payable to any person on the basis of the compensation and years of service of an individual by reason of the provisions of subsection (a), (b), or (c) of this section if, and to the extent that, such annuity or other benefit would duplicate a benefit payable to such person on the basis of such compensation and years of service under a provision of the Social Security Act [42 U.S.C. 301 et seq.], or any other Act of Congress, which becomes effective after December 31, 1974.

(2) No annuity shall be payable to a person by reason of subsection (a) or (b) of this section unless the individual upon whose compensation and years of service such annuity would be based will have (A) completed ten years of service (or five or more years of service, all of which accrues after December 31, 1995), and (B) in the case of a survivor, had a current connection with the railroad industry at the time of his death.

(3) If the Social Security Act [42 U.S.C. 301 et seq.] is amended after December 31, 1974, to remove any, or all, restriction on the receipt of more than one monthly insurance benefit thereunder, annuity amounts provided a person under section 231b(h), 231c(e), or 231c(h) of this title, or under section 204(a)(3), 204(a)(4), 206(3), or 207(3) of title II of this Act, shall be reduced (but not below zero) by the amount of any annuity provided such person under this subchapter by reason of such amendment.

(4) If and to the extent that an annuity or other benefit payable to a person by reason of the provisions of subsection (a), (b), or (c) of this section duplicates an annuity or other benefit then payable to such person under other provisions of this subchapter, such annuity or other benefit then payable under other provisions of this subchapter shall be reduced (but not below zero) by the amount of the annuity or other benefit payable by reason of subsection (a), (b), or (c).