For words that have only 3 letters, there isn't any 4th letter. Such as with the word “incorporate”, there aren't any additional letters Later on and thus have to be the word "insert". The word “addict” is from the BIP39 wordlist however you would've utilised “addi” for “addict”. Using BIP44 https://thejillist.com/story8955050/the-invalid-bip39-phrase-diaries