For words that have only three letters, there isn't a 4th letter. For instance with the word “insert”, there are no far more letters Later on and therefore should be the word "insert". The word “addict” is in the BIP39 wordlist however , you would've applied “addi” for “addict”. By https://friendlybookmark.com/story18930834/the-invalid-bip39-phrase-diaries