For words that only have three letters, there is not any 4th letter. One example is with the word “include”, there isn't any more letters afterwards and thus have to be the word "add". The word “addict” is from the BIP39 wordlist however you would've employed “addi” for “addict”. BIP39 https://tetrabookmarks.com/story18852674/the-fact-about-valid-bip39-seed-phrase-that-no-one-is-suggesting