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 calendar quarter that has not begun;
A calendar quarter that begins after the quarter of your death;
A calendar quarter that has already been counted as a QC; or
A calendar quarter that is included in a period of disability established for you, unless—
The quarter is the first or the last quarter of this period; or
The period of disability is not taken into consideration (see § 404.320(a)).