For words that only have 3 letters, there's no 4th letter. Such as with the word “include”, there aren't any additional letters afterwards and so must be the word "add". The word “addict” is during the BIP39 wordlist however, you would've utilised “addi” for “addict”. In this post we’ll share https://bookmarkcork.com/story19584267/the-basic-principles-of-bip39-passphrase-generator