For words that only have 3 letters, there isn't any 4th letter. For instance with the word “insert”, there won't be any additional letters Later on and so have to be the word "add". The word “addict” is during the BIP39 wordlist however you would've applied “addi” for “addict”. A https://sound-social.com/story9052968/bip39-seed-phrase-fundamentals-explained