For words that have only 3 letters, there's no 4th letter. One example is with the word “include”, there are no a lot more letters afterwards and thus needs to be the word "insert". The word “addict” is within the BIP39 wordlist however you would've made use of “addi” for https://bookmarkplaces.com/story18799188/the-greatest-guide-to-seed-phrase-bip39