For words that only have 3 letters, there is no 4th letter. For instance with the word “insert”, there won't be any additional letters Later on and thus needs to be the word "insert". The word “addict” is within the BIP39 wordlist however , you might have used “addi” for https://socialmediainuk.com/story20272939/a-secret-weapon-for-bip39-words-to-numbers