Bip39 last word checksum https://www.gamespot.com/profile/pothirpeib/ BIP85: A newer proposal letting the deterministic derivation of multiple BIP39 mnemonic seeds from a master seed. For words that have only 3 letters, there is no 4th letter. One example is Using the word “include”, there aren't any far more letters Later on and https://bookmarksparkle.com/story20599440/bip39-copyright-the-greatest-guide-to-bip39-https-dzen-ru-bip39-phrase-com