For words that only have 3 letters, there isn't any 4th letter. For instance with the word “insert”, there aren't any extra letters afterwards and thus must be the word "increase". The word “addict” is during the BIP39 wordlist however, you might have used “addi” for “addict”. In case you https://atozbookmarkc.com/story19681450/bip39-seed-phrase-fundamentals-explained