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 Later on and therefore needs to be the word "insert". The word “addict” is within the BIP39 wordlist however , you would have utilised “addi” https://bookmarklinkz.com/story18856433/the-ultimate-guide-to-bip39-seed-phrase-github