Sorry, I didn't make the connection between the conditional formatting and
your other question. Now, you do not need to use COUNTIF.3D since you are
not 'making it work across multiple worksheets'.
One solution, found here:
http://tinyurl.com/24pp5
is to enter your countif formula referring to some named range,
e.g.
conditional format: =COUNTIF(DDA,A5)>1 and set your format.
then jump over to DDA sheet, select A4:A323, and go to insert>name>define>
and enter DDA, and apply.
Now jump back over to your sheet, and your format should be applied (if
true).