Excel 2007 : Problem IF and COUNTIFS formula

Hi,
Am trying to count unique names from a list which match a specific criteria and returns 1. Ive summarised below with a detailed example attached
col_A: name
col_B: dd/mm/yyyy (date)
col_C: formula

Please Login or Register  to view this content.

col_D: formula

Please Login or Register  to view this content.

However, for certain names I get double counts in col_D. I think the problem is to do with the dates in col_B, when they are the same but one month out i.e. 14/02/11 and 14/03/11 (and only for Mar never for Jan) I get a duplicate counts but I cant find a way around it.

Your help would be much appreciated!
Thanks

If you only want to include Feb-11 you need to test that current record is Feb-11.
The reason you get "0" in Jan but not Mar is that at point of Jan there are no Feb records... by March there can be.

Assuming above assumptions are correct:

Please Login or Register  to view this content.