For words that have only three letters, there isn't a 4th letter. As an example with the word “insert”, there aren't any extra letters afterwards and so needs to be the word "incorporate". The word “addict” is in the BIP39 wordlist however, you would've used “addi” for “addict”. When you https://bookmark-nation.com/story18701794/top-guidelines-of-bip39-word-list-pdf