For words that only have 3 letters, there is not any 4th letter. For instance with the word “incorporate”, there won't be any far more letters afterwards and therefore have to be the word "include". The word “addict” is inside the BIP39 wordlist however, you would've made use of “addi” https://bookmark-template.com/story23870072/the-basic-principles-of-bip39-passphrase-generator