For words that have only three letters, there isn't a 4th letter. By way of example with the word “increase”, there are no extra letters afterwards and so should be the word "include". The word “addict” is during the BIP39 wordlist however, you would have utilised “addi” for “addict”. The https://bookmarkforce.com/story19695871/little-known-facts-about-bip39-words