For words that have only 3 letters, there isn't any 4th letter. For example with the word “insert”, there are no additional letters Later on and so have to be the word "add". The word “addict” is from the BIP39 wordlist however you would've used “addi” for “addict”. You have https://bookmark-nation.com/story18795295/a-review-of-bip39-passphrase