Using date fields as reference with COUNTIFS?

Hi all,

Attached is example workbook with two instances of what I thought might yield the same result.
In the tab SUMDATA, I am trying to use the dates in rows 2 and 3 as the reference for a COUNTIFS.

For the column with the dates for April 2015 ( the result in D4), the formula works fine with this reference:

=COUNTIFS(COHORT!$C:$C,">=1/4/15",COHORT!$C:$C,"<=30/4/15")

but that means I have to reference the start and end dates manually. I'd like a solution like the one in the column for March 2015 (the result in cell C4), for which this code doesn't work:

=COUNTIFS(COHORT!$C:$C,"C2",COHORT!$C:$C,"C3")

Does anyone know a way to reference cells C2 and C3 to be part of the criteria for COUNTIFS?

Hope that makes sense!

cheers
Pete