For words that have only three letters, there's no 4th letter. For example with the word “insert”, there aren't any much more letters afterwards and so have to be the word "include". The word “addict” is during the BIP39 wordlist however, you would have utilised “addi” for “addict”. Standard recovery https://kingslists.com/story20121934/invalid-bip39-phrase-things-to-know-before-you-buy