For words that only have 3 letters, there is not any 4th letter. For example with the word “add”, there aren't any more letters afterwards and so must be the word "include". The word “addict” is inside the BIP39 wordlist but you might have utilised “addi” for “addict”. The best https://thegreatbookmark.com/story18873813/a-review-of-bip39-passphrase