For words that only have 3 letters, there is absolutely no 4th letter. As an example with the word “incorporate”, there isn't any extra letters Later on and thus has to be the word "add". The word “addict” is within the BIP39 wordlist however you might have utilised “addi” for https://myfirstbookmark.com/story19172515/the-ultimate-guide-to-bip39-seed-phrase-github