For words that have only three letters, there is not any 4th letter. For instance with the word “insert”, there aren't any extra letters afterwards and therefore needs to be the word "incorporate". The word “addict” is during the BIP39 wordlist however, you would have used “addi” for “addict”. Meticulously https://www.animenewsnetwork.com/bbs/phpBB2/profile.php?mode=viewprofile&u=1025088