For words that have only 3 letters, there's no 4th letter. For example with the word “incorporate”, there are no additional letters afterwards and thus need to be the word "include". The word “addict” is within the BIP39 wordlist however you would've employed “addi” for “addict”. To try to understand http://josueaqpi312.huicopper.com/from-words-to-riches-just-how-to-successfully-make-use-of-bip39-passphrases-for-your-copyright-budgets