For words that only have three letters, there's no 4th letter. One example is with the word “incorporate”, there are no far more letters Later on and so need to be the word "include". The word “addict” is from the BIP39 wordlist however you would have used “addi” for “addict”. https://hylistings.com/story19962902/considerations-to-know-about-bip39-seed-phrase-generator