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

=IF(B2="","Blank",TEXT(B2,"mmm-yy"))

col_D: formula

=IF(COUNTIFS($A$2:A2,A2,$C$2:C2,"Feb-11")=1,1,"0")

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