For words that only have three letters, there is not any 4th letter. Such as with the word “insert”, there won't be any a lot more letters Later on and therefore has to be the word "include". The word “addict” is from the BIP39 wordlist however , you might have https://bookmarkusers.com/story19294412/new-step-by-step-map-for-bip39-english-words