For words that only have three letters, there is not any 4th letter. As an example with the word “increase”, there isn't any extra letters afterwards and thus needs to be the word "increase". The word “addict” is from the BIP39 wordlist however, you might have employed “addi” for “addict”. https://highkeysocial.com/story4526358/the-ultimate-guide-to-bip39-seed-phrase-github