For words that have only 3 letters, there is not any 4th letter. For example with the word “add”, there won't be any a lot more letters Later on and so has to be the word "include". The word “addict” is while in the BIP39 wordlist however you might have https://bookmarksknot.com/story20662885/detailed-notes-on-copyright-wallet-seed-phrase-out-of-bip39