For words that have only 3 letters, there is no 4th letter. As an example with the word “increase”, there isn't any additional letters Later on and thus should be the word "include". The word “addict” is within the BIP39 wordlist however you would've employed “addi” for “addict”. BIP39 and https://esocialmall.com/story4229523/the-basic-principles-of-bip39-passphrase-generator