For words that have only three letters, there's no 4th letter. For example with the word “incorporate”, there are no more letters Later on and therefore must be the word "insert". The word “addict” is within the BIP39 wordlist however , you might have made use of “addi” for “addict”. https://minibookmarking.com/story18920664/helping-the-others-realize-the-advantages-of-bip39-mnemonic-phrase-tool