Thanks Aladin, your options work wonderfully. For the benefit of others,
the final formula I chose to use was:
=SUM(IF(FREQUENCY(IF(($B$2:$B$16-DAY($B$2:$B$16)+1=D2)*($A$2:$A$16<""),MATCH($A$2: $A$16,$A$2:$A$16,0)),ROW($B$2:$B$16))0,1))


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Flystar
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