For words that have only three letters, there is absolutely no 4th letter. One example is with the word “incorporate”, there are no additional letters afterwards and therefore should be the word "insert". The word “addict” is during the BIP39 wordlist however you would have utilized “addi” for “addict”. This https://agendabookmarks.com/story18757356/top-latest-five-bip39-seed-phrase-mnemonics-generator-urban-news