For words that only have 3 letters, there is not any 4th letter. For instance with the word “add”, there isn't any far more letters afterwards and thus must be the word "increase". The word “addict” is within the BIP39 wordlist however you would have utilised “addi” for “addict”. Standard https://total-bookmark.com/story18830351/fascination-about-invalid-bip39-phrase