For words that have only 3 letters, there isn't any 4th letter. For instance with the word “add”, there are no extra letters Later on and thus need to be the word "include". The word “addict” is while in the BIP39 wordlist however you might have employed “addi” for “addict”. https://businessbookmark.com/story5074965/examine-this-report-on-bip39-passphrase