For words that only have 3 letters, there isn't any 4th letter. For instance with the word “add”, there aren't any extra letters Later on and therefore needs to be the word "insert". The word “addict” is during the BIP39 wordlist however , you might have made use of “addi” https://bookmarkcork.com/story19630185/a-review-of-bip39-passphrase