For words that only have three letters, there isn't a 4th letter. One example is with the word “include”, there isn't any far more letters Later on and so have to be the word "add". The word “addict” is from the BIP39 wordlist but you would've utilised “addi” for “addict”. https://optimusbookmarks.com/story18758972/the-basic-principles-of-bip39-passphrase-generator