For words that have only 3 letters, there isn't a 4th letter. For instance with the word “include”, there won't be any more letters afterwards and so should be the word "add". The word “addict” is from the BIP39 wordlist however, you would've used “addi” for “addict”. A different advantage https://bookmarkworm.com/story19429459/considerations-to-know-about-bip39-seed-phrase-generator