For words that have only 3 letters, there's no 4th letter. For instance with the word “incorporate”, there won't be any much more letters afterwards and thus should be the word "include". The word “addict” is in the BIP39 wordlist but you would have utilised “addi” for “addict”. Art is https://thebookpage.com/story4191359/top-guidelines-of-bip39-word-list-pdf