For words that only have 3 letters, there is not any 4th letter. One example is with the word “include”, there aren't any much more letters Later on and so needs to be the word "insert". The word “addict” is while in the BIP39 wordlist however, you would have used https://webcastlist.com/story19968042/the-fact-about-valid-bip39-seed-phrase-that-no-one-is-suggesting