For words that have only three letters, there isn't a 4th letter. As an example with the word “increase”, there isn't any more letters Later on and so must be the word "insert". The word “addict” is within the BIP39 wordlist however , you would have applied “addi” for “addict”. http://josueaqpi312.huicopper.com/from-words-to-riches-just-how-to-successfully-make-use-of-bip39-passphrases-for-your-copyright-budgets