For words that have only 3 letters, there isn't a 4th letter. One example is with the word “include”, there are no extra letters Later on and therefore need to be the word "incorporate". The word “addict” is inside the BIP39 wordlist however you would have made use of “addi” https://webnowmedia.com/story4879554/helping-the-others-realize-the-advantages-of-bip39-seed-phrase-mnemonics-generator