For words that only have three letters, there isn't any 4th letter. For example with the word “incorporate”, there aren't any extra 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”. A seed https://toplistar.com/story20668807/the-definitive-guide-to-bip39-seed-phrase