For words that only have three letters, there is absolutely no 4th letter. One example is with the word “incorporate”, there won't be any a lot more letters Later on and so have to be the word "include". The word “addict” is in the BIP39 wordlist however, you would have https://1001bookmarks.com/story18691584/how-much-you-need-to-expect-you-ll-pay-for-a-good-bip39-definition