For words that have only three letters, there is absolutely no 4th letter. For example with the word “include”, there are no far more letters afterwards and so must be the word "increase". The word “addict” is during the BIP39 wordlist however , you would have utilised “addi” for “addict”. https://hyperbookmarks.com/story18945536/the-basic-principles-of-bip39-passphrase-generator