For words that only have three letters, there's no 4th letter. For example with the word “increase”, there won't be any additional letters Later on and therefore need to be the word "include". The word “addict” is during the BIP39 wordlist however you would've employed “addi” for “addict”. In this https://ok-social.com/story4400099/5-essential-elements-for-bip39-explained