For words that only have three letters, there is not any 4th letter. For instance with the word “include”, there won't be any more letters afterwards and so needs to be the word "increase". The word “addict” is during the BIP39 wordlist however , you might have used “addi” for https://baidubookmark.com/story18693094/helping-the-others-realize-the-advantages-of-bip39-mnemonic-phrase-tool