For words that only have 3 letters, there is no 4th letter. As an example with the word “add”, there won't be any a lot more letters Later on and therefore should be the word "insert". The word “addict” is while in the BIP39 wordlist but you might have utilised https://bookmarklogin.com/story18937205/getting-my-bip39-words-to-numbers-to-work