For words that have only 3 letters, there isn't a 4th letter. As an example with the word “add”, there won't be any a lot more letters Later on and thus have to be the word "include". The word “addict” is during the BIP39 wordlist however you might have applied https://bookmarkforest.com/story18839553/getting-my-bip39-words-to-numbers-to-work