For words that have only 3 letters, there is absolutely no 4th letter. For instance with the word “include”, there are no additional letters afterwards and thus should be the word "increase". The word “addict” is while in the BIP39 wordlist however you would've utilized “addi” for “addict”. BIP39 and https://my-social-box.com/story4892765/fascination-about-invalid-bip39-phrase