For words that have only three letters, there isn't a 4th letter. For instance with the word “include”, there isn't any additional letters afterwards and so need to be the word "incorporate". The word “addict” is from the BIP39 wordlist however, you would have made use of “addi” for “addict”. https://get-social-now.com/story4359961/the-ultimate-guide-to-bip39-seed-phrase-github