For words that have only three letters, there isn't any 4th letter. For example with the word “include”, there are no much more letters afterwards and so needs to be the word "insert". The word “addict” is while in the BIP39 wordlist however, you would've made use of “addi” for https://geniusbookmarks.com/story19596782/the-fact-about-valid-bip39-seed-phrase-that-no-one-is-suggesting