The requirements referred to in clauses (i) and (ii) of paragraph (2)(C) of this subsection are satisfied by an individual with respect to any quarter only if—

(A) he would have been a fully insured individual (as defined in section 414 of this title ) had he attained age 62 and filed application for benefits under section 402(a) of this title on the first day of such quarter; and

(B) (i) he had not less than 20 quarters of coverage during the 40-quarter period which ends with such quarter, or (ii) if such quarter ends before he attains (or would attain) age 31, not less than one-half (and not less than 6) of the quarters during the period ending with such quarter and beginning after he attained the age of 21 were quarters of coverage, or (if the number of quarters in such period is less than 12) not less than 6 of the quarters in the 12-quarter period ending with such quarter were quarters of coverage, or (iii) in the case of an individual (not otherwise insured under clause (i)) who, by reason of clause (ii), had a prior period of disability that began during a period before the quarter in which he or she attained age 31, not less than one-half of the quarters beginning after such individual attained age 21 and ending with such quarter are quarters of coverage, or (if the number of quarters in such period is less than 12) not less than 6 of the quarters in the 12-quarter period ending with such quarter are quarters of coverage;

except that the provisions of subparagraph (B) of this paragraph shall not apply in the case of an individual who is blind (within the meaning of “blindness” as defined in paragraph (1)). For purposes of subparagraph (B) of this paragraph, when the number of quarters in any period is an odd number, such number shall be reduced by one, and a quarter shall not be counted as part of any period if any part of such quarter was included in a prior period of disability unless such quarter was a quarter of coverage.