If an employee legally adopts his or her grandchild or the spouse's grandchild after he could become entitled to an old age or disability benefit under the Social Security Act (treating his or her railroad compensation as wages under that Act), the grandchild is considered dependent on the employee during the employee's lifetime only if the requirements in paragraphs (a) and (b), and either (c) or (d) of this section are met:

(a) The grandchild is adopted in the United States.

(b) The grandchild began living with the employee before the grandchild attained age 18.

(c) The grandchild is living with the employee in the United States and receives at least one-half of his or her support from the employee for the year before the month in which—

(1) The employee's annuity was increased under the social security overall minimum provision by including the grandchild; or

(2) The employee could become entitled to a social security benefit as described above; or

(3) The employee becomes entitled to a period of disability which continues until he or she could become entitled to a social security benefit as described above.

(d) In the case of a grandchild born within the one-year period referred to in paragraph (c) of this section, at the close of such period the child must have been living with and have been receiving at least one-half of his or her support from the employee for substantially all of the period that began on the date the grandchild was born. “Substantially all” is defined in §222.53.