(b)
Each annuity payable to or on behalf of an eligible child (other than a child who is incapable of supporting himself because of a mental defect or physical incapacity existing before his eighteenth birthday) as defined in section
1435
(2)(B) of this title who is at least eighteen years of age and pursuing a full-time course of study or training at a recognized educational institution, accrues—
(1)
as of the first day of the month in which the member upon whose pay the annuity is based dies, if the eligible child’s eighteenth birthday occurs in the same or a preceding month.
(2)
as of the first day of the month in which the eighteenth birthday of an eligible child occurs, if the member upon whose pay the annuity is based died in a preceding month.
(3)
as of the first day of the month in which a child first becomes or again becomes eligible, if that eligible child’s eighteenth birthday and the death of the member upon whose pay the annuity is based both occurred in a preceding month or months.
However, no such annuity is payable or accrues for any month before November 1, 1968.