For words that have only 3 letters, there isn't a 4th letter. By way of example with the word “include”, there isn't any extra letters afterwards and thus should be the word "insert". The word “addict” is inside the BIP39 wordlist however, you would have made use of “addi” for https://bookmarkswing.com/story21220881/facts-about-bip39-seed-phrase-github-revealed