For words that have only 3 letters, there is no 4th letter. One example is with the word “include”, there won't be any much more letters afterwards and therefore have to be the word "include". The word “addict” is during the BIP39 wordlist however you would've employed “addi” for “addict”. https://todaybookmarks.com/story18961080/getting-my-bip39-words-to-numbers-to-work