For words that only have three letters, there is not any 4th letter. One example is with the word “add”, there won't be any additional letters afterwards and thus must be the word "insert". The word “addict” is inside the BIP39 wordlist however , you would have utilized “addi” for https://bookmarkity.com/story18983883/the-ultimate-guide-to-bip39-seed-phrase-github