For words that have only 3 letters, there isn't a 4th letter. For instance with the word “insert”, there are no much more letters Later on and so have to be the word "include". The word “addict” is during the BIP39 wordlist however you would've applied “addi” for “addict”. The https://bookmarksaifi.com/story18922752/top-guidelines-of-bip39-word-list-pdf