For words that have only 3 letters, there is no 4th letter. One example is with the word “include”, there are no far more letters afterwards and so need to be the word "include". The word “addict” is in the BIP39 wordlist however, you would have utilised “addi” for “addict”. https://210list.com/story19363523/the-definitive-guide-to-bip39-seed-phrase