For words that only have 3 letters, there isn't any 4th letter. For instance with the word “add”, there aren't any more letters afterwards and so needs to be the word "include". The word “addict” is in the BIP39 wordlist however , you would've employed “addi” for “addict”. By adhering https://ok-social.com/story4472261/facts-about-bip39-seed-phrase-github-revealed