Count Unique Values Between Two Dates?

I want to count the unique values between 2 dates. He only needs to count the values that match 2 criteria. I want to know how many unique orders were place between 01/10/2012 and 30/09/2013.

In my Data sheet:
Colomn X: Customer name
Colomn D: Status
Colomn AH: Date of order (Day/Month/Year)

I want to count the unique values in Colomn O: Ordernumbers

This is what I already have:

=SUM(--(FREQUENCY(IF(Data!$X:$X=$A4;IF(Data!$D:$D="BOOKED";Data!$O:$O));Data!$O:$O)>0))

This formula is working. He counts the unique values in colomn O that meet the 2 criteria (Status = "BOOKED"; Customer = A4).

But I don't know how the add the date range in this formula. I want him to take only the values that are between 01/10/2012 and 30/09/2013.