Count Unique Text String

I am seeking help on below mentioned formula.

=IF($A4="","",SUMPRODUCT(--(Master!$C:$C="Dental"),--(Master!$K:$K>=AR6),--(Master!$K:$K<=AR5)))

Details:

1. I am counting a unique i.e. Dental in my master sheet in column C.
2. Then it count the values greater or equal to 0:29 and less then or equal to 0:20


But the issue is is it not counting the values which is equal to 0:29. what is the problem can any one help me please.