For words that only have 3 letters, there isn't a 4th letter. One example is with the word “include”, there won't be any far more letters afterwards and therefore has to be the word "increase". The word “addict” is from the BIP39 wordlist but you would've utilized “addi” for “addict”. https://onelifesocial.com/story4842008/phrases-with-bit-an-overview