For words that only have three letters, there isn't a 4th letter. As an example with the word “add”, there isn't any more letters Later on and so have to be the word "add". The word “addict” is during the BIP39 wordlist however you would've utilized “addi” for “addict”. If https://hyperbookmarks.com/story18899821/the-definitive-guide-to-bip39-seed-phrase