For words that only have 3 letters, there's no 4th letter. One example is with the word “include”, there are no far more letters afterwards and so should be the word "add". The word “addict” is from the BIP39 wordlist however , you would have applied “addi” for “addict”. Artwork https://socialislife.com/story4357000/not-known-factual-statements-about-bip39-explained