Sort -u Function Command Not Working

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http://unix.stackexchange.com – As you can see in the picture attached screen shot After i used the sort command to sort a VERY large wordlist file i then split them up using the Split command. From there i confirmed that the listed words are in a-z order. I then ran the sort -u command and noticed that it was not removing unique words. (is was removing some as i could see the files were a little smaller....but not all what am i doing wrong? Overall goal: my over all goal is to take all my wordlists and put them into one large file (25gig), then sort and remove any unique words (cutting this by 40% or so) and then split (HowTos)