For words that only have 3 letters, there is not any 4th letter. For example with the word “add”, there aren't any additional letters Later on and so have to be the word "incorporate". The word “addict” is inside the BIP39 wordlist however, you would have made use of “addi” https://bookmarkja.com/story20808081/examine-this-report-on-bip39-passphrase