For words that have only 3 letters, there isn't any 4th letter. For instance with the word “add”, there won't be any far more letters Later on and so have to be the word "insert". The word “addict” is from the BIP39 wordlist but you would've applied “addi” for “addict”. https://naturalbookmarks.com/story19038379/fascination-about-bip39-english-words