For words that only have 3 letters, there isn't a 4th letter. By way of example with the word “include”, there are no additional letters Later on and therefore should be the word "insert". The word “addict” is inside the BIP39 wordlist however you might have made use of “addi” https://bookmarksbay.com/story18862821/top-guidelines-of-bip39-word-list-pdf