Morning all,
I've got a working Sum Frequency formula which counts unique matches.
=SUM(--(FREQUENCY(IF((Driver!$A$2:$A$1973='Data Selection'!$A$1)*(Driver!$G$2:$G$1973="No"),MATCH(Driver!$D$2:$D$1973,Driver!$D$2:$D$1973,0)),ROW(Driver!$D$2:$D$1973)-ROW(OFFSET(Driver!$D$1,1,))+1)>0))
It works...