For words that have only 3 letters, there's no 4th letter. By way of example with the word “include”, there won't be any additional letters afterwards and thus should be the word "add". The word “addict” is within the BIP39 wordlist however , you might have utilized “addi” for “addict”. https://admiralbookmarks.com/story19174707/facts-about-bip39-seed-phrase-github-revealed