For words that have only three letters, there isn't a 4th letter. By way of example with the word “add”, there won't be any far more letters Later on and so need to be the word "include". The word “addict” is in the BIP39 wordlist but you might have used https://bookmark-nation.com/story18795399/new-step-by-step-map-for-bip39-english-words