When was bip39 introduced https://telegra.ph/Producing-Custom-Bitcoin-Addresses-A-Take-A-Look-At-BIP39-Strategies-06-28 Checksum development: A checksum is created from this entropy using SHA-256 hashing, which assists verify the mnemonic's integrity later. For words that only have 3 letters, there isn't any 4th letter. One example is Using the word “insert”, there won't be any extra ... https://socialaffluent.com/story5909406/bip39-adalah-5-tips-about-bip39-checksum-you-can-use-today-https-cutt-ly-uryc5rw7