Count duplicate text values in columns whilst ignoring/excluding certain values

Hi all,

I'm struggling with an array formula at the moment and was hoping someone here would be able to help out. The formula I've currently got (see below) is working well at counting the duplicate text values in columns, however, I now need to exclude certain specified text values from the formula. The formula I'm currently using is:

{=SUM(IF(FREQUENCY(IF(A1:A8<>"",MATCH(A1:A8,A1:A8,0)),ROW(A1:A8)-ROW(A1)+1)>1,1))}

I have attached a simplified excel file in relation to the above formula. What I am trying to achieve is for the array formula to count all duplicate values, expect for any text values which equal both "e" and "f".

Hopefully I've provided enough information for someone to help out, and looking forward to hearing from some formula wizards who can work their magic on my problem.

Many thanks,

Adam