For words that have only 3 letters, there isn't any 4th letter. By way of example with the word “increase”, there won't be any a lot more letters afterwards and thus must be the word "include". The word “addict” is while in the BIP39 wordlist but you might have used https://pr1bookmarks.com/story19018637/getting-my-bip39-words-to-numbers-to-work