For words that have only three letters, there is absolutely no 4th letter. Such as with the word “include”, there isn't any extra letters afterwards and therefore have to be the word "insert". The word “addict” is inside the BIP39 wordlist but you would have employed “addi” for “addict”. The https://agendabookmarks.com/story18783221/the-basic-principles-of-bip39-passphrase-generator