For words that only have three letters, there isn't a 4th letter. For instance with the word “add”, there isn't any much more letters Later on and thus needs to be the word "insert". The word “addict” is within the BIP39 wordlist however , you would have made use of https://socialmediainuk.com/story20227971/the-fact-about-valid-bip39-seed-phrase-that-no-one-is-suggesting