For words that only have three letters, there isn't a 4th letter. One example is with the word “insert”, there aren't any a lot more letters Later on and so needs to be the word "insert". The word “addict” is from the BIP39 wordlist however you would have applied “addi” https://socialrator.com/story9437832/detailed-notes-on-copyright-wallet-seed-phrase-out-of-bip39