For words that have only 3 letters, there's no 4th letter. For instance with the word “incorporate”, there are no extra letters afterwards and thus has to be the word "add". The word “addict” is inside the BIP39 wordlist however , you would've used “addi” for “addict”. Standard recovery phrases https://easiestbookmarks.com/story19690106/5-essential-elements-for-bip39-explained