For words that have only 3 letters, there isn't a 4th letter. As an example with the word “insert”, there won't be any much more letters Later on and therefore should be the word "include". The word “addict” is within the BIP39 wordlist however you would have made use of https://bookmark-media.com/story18915387/the-fact-about-valid-bip39-seed-phrase-that-no-one-is-suggesting