For words that have only three letters, there isn't any 4th letter. For example with the word “add”, there are no additional letters Later on and so must be the word "incorporate". The word “addict” is while in the BIP39 wordlist however you would have utilized “addi” for “addict”. bip39-phrase.com https://opensocialfactory.com/story19283486/fascination-about-invalid-bip39-phrase