For words that have only 3 letters, there isn't a 4th letter. As an example with the word “include”, there isn't any far more letters afterwards and therefore need to be the word "increase". The word “addict” is within the BIP39 wordlist however you would have employed “addi” for “addict”. https://top100bookmark.com/story19070855/considerations-to-know-about-bip39-seed-phrase-generator