unfortunately the way the original spreadsheet is set out it is not
suitable to add 'helper cells' on each row. ive checked with the data
owner and they say its ok to use the first date in a cell, so ended up
using a sumproduct to do counts of dates:-
=SUMPRODUCT(--(((IF(ISERROR(LEFT('Input Data'!$J$7:$J$26,(FIND("
",'Input Data'!$J$7:$J$26)-1))*1),'Input
Data'!$J$7:$J$26,LEFT('Input Data'!$J$7:$J$26,(FIND("
",'Input Data'!$J$7:$J$26)-1))*1))=A2)*((IF(ISERROR(LEFT('Input
Data'!$J$7:$J$26,(FIND("
",'Input Data'!$J$7:$J$26)-1))*1),'Input
Data'!$J$7:$J$26,LEFT('Input Data'!$J$7:$J$26,(FIND("
",'Input Data'!$J$7:$J$26)-1))*1))<A2+7)))