For words that have only 3 letters, there's no 4th letter. For instance with the word “increase”, there aren't any extra letters Later on and thus need to be the word "include". The word “addict” is during the BIP39 wordlist however, you would have utilised “addi” for “addict”. How to https://pageoftoday.com/story4256502/5-essential-elements-for-bip39-explained