countif - issue (no duplicates)

Hello

Can someone tell me what im doing wrong with this?

=IF(ROWS($52:52)>COUNTIF(Data!$CX$12:$CX$75,Calculations!$E$51),"",INDEX(Data!$CW$12:$CW$75,SMALL(INDEX(ROW(Data!$CX$12:$CX$75)+(Data!$CX$12:$CX$75<>Calculations!$E$51)*10^10,0),ROWS($52:52))))

there should be a total of 13 entries.

so after 13 entries, the formula should give a zero result.....but this appears to not be happening, any ideas why?

basically, this lets me not get any duplicate values from the list taht i have. thx you so much!