For words that only have three letters, there isn't any 4th letter. One example is with the word “increase”, there are no far more letters afterwards and so should be the word "add". The word “addict” is while in the BIP39 wordlist however, you would've used “addi” for “addict”. You https://thebookmarklist.com/story18853233/the-basic-principles-of-bip39-passphrase-generator