Bip39 Checksum. Since the 24th is often a checksum word, a list of 8 valid candidate words are calculated using the Python script 24thword.py. For words that only have 3 letters, there isn't a 4th letter. For instance With all the word “add”, there isn't any additional letters Later on https://exceeddirectory.com/listings601353/bip39-mnemonic-generator-https-linktr-ee-bip39-the-greatest-guide-to-bip39-list