For words that only have 3 letters, there isn't any 4th letter. One example is with the word “insert”, there aren't any much more letters Later on and so have to be the word "incorporate". The word “addict” is while in the BIP39 wordlist however you might have employed “addi” https://bookmarkstime.com/story19570555/top-guidelines-of-bip39-word-list-pdf