For words that have only 3 letters, there is no 4th letter. For example with the word “incorporate”, there aren't any much more letters afterwards and so must be the word "add". The word “addict” is inside the BIP39 wordlist however , you would've applied “addi” for “addict”. Protection: Any https://www.tumblr.com/generalllamacolor/772952501127380992/opening-the-globe-of-bip39-a-comprehensive-guide