This section applies when we credit you with quarters of coverage (QCs) under § 404.141 for calendar years before 1978 and under § 404.143 for calendar years after 1977. We cannot credit you with a QC for—
(a) A calendar quarter that has not begun;
(b) A calendar quarter that begins after the quarter of your death;
(c) A calendar quarter that has already been counted as a QC; or
(d) A calendar quarter that is included in a period of disability established for you, unless—
(1) The quarter is the first or the last quarter of this period; or
(2) The period of disability is not taken into consideration (see § 404.320(a)).