For words that only have three letters, there is no 4th letter. One example is with the word “add”, there isn't any a lot more letters Later on and so has to be the word "incorporate". The word “addict” is within the BIP39 wordlist however , you would've applied “addi” https://throbsocial.com/story20669468/top-guidelines-of-bip39-word-list-pdf