For words that only have 3 letters, there isn't any 4th letter. One example is with the word “insert”, there won't be any a lot more letters Later on and so have to be the word "add". The word “addict” is during the BIP39 wordlist however, you might have employed https://thebookmarklist.com/story18978051/how-much-you-need-to-expect-you-ll-pay-for-a-good-bip39-definition