I've got a column of client company names and because it is based from accounts, the companies names appear many times. I just need to populate a new column with unique names, so I have found a forumula to do this:

=INDEX($A$2:$A$20, MATCH(0, COUNTIF($B$1:B1, $A$2:$A$20), 0))

However when I do this, I CtrlShiftEnter and drag to copy that down, and it's just a copy of the original list - client names are appearing on my new list multiple times. I don't see how this doesn't work... any help? I'm using 2013.