For words that only have 3 letters, there is absolutely no 4th letter. Such as with the word “insert”, there aren't any much more letters afterwards and so have to be the word "include". The word “addict” is during the BIP39 wordlist however , you might have applied “addi” for https://bookmarkspedia.com/story4504507/the-basic-principles-of-bip39-passphrase-generator