For words that have only three letters, there's no 4th letter. One example is with the word “insert”, there isn't any far more letters Later on and thus has to be the word "include". The word “addict” is in the BIP39 wordlist however you would've employed “addi” for “addict”. By https://mediajx.com/story21496849/helping-the-others-realize-the-advantages-of-bip39-mnemonic-phrase-tool