For words that only have three letters, there isn't a 4th letter. For example with the word “incorporate”, there isn't any extra letters afterwards and so needs to be the word "include". The word “addict” is inside the BIP39 wordlist however you would've made use of “addi” for “addict”. This https://pr1bookmarks.com/story19005622/the-ultimate-guide-to-bip39-seed-phrase-mnemonics-generator