For words that have only 3 letters, there isn't a 4th letter. For instance with the word “add”, there won't be any more letters Later on and thus must be the word "add". The word “addict” is in the BIP39 wordlist however, you would've utilized “addi” for “addict”. A seed https://maximusbookmarks.com/story18961599/the-ultimate-guide-to-bip39-seed-phrase-github