Index Array return values between dates

Hi

I have a formula (see below) which returns data from an array perfectly, it is based on concatenating a 2 character code and a specific date (displayed as an integer)

=INDEX(Sheet1!A:A,SMALL(IF(concat(Sheet1!$Q$2:$Q,Sheet1!$P$2:$P)=$A$4,ROW(Sheet1!$Q$2:$Q)),ROWS(D$3:D3)))

Cell A4 contains the argument which is a concatenation of the 2 digit character code plus the date , therefore 'KB' + 11/09/2017 would equate to "KB42989" this in turn relates to concat(Sheet1!$Q$2:$Q,Sheet1!$P$2:$P)=$A$4 in the formula.

I would like to make the argument based between dates i.e. 11/09/17 to 15/09/17 would be KB42989 to KB42993, i've tried changing my argument to first look for the unique character code, then equal to or greater than 42989 and less than 42993.

There is probably a much easier way of achieving this but i can't work it out.

Many thanks

Pros

=INDEX(Sheet1!A:A,SMALL(IF((Sheet1!$Q$2:$Q="KB")*(MATCH(Sheet1!$P$2:$P,$A$3:$A$5)=2),ROW(Sheet1!$Q$2:$Q)),ROWS(D$3:D3)))
a3=0, a4=11/09/17, a5=15/09/17,
and much faster