For words that have only 3 letters, there isn't a 4th letter. As an example with the word “include”, there isn't any much more letters afterwards and thus should be the word "insert". The word “addict” is while in the BIP39 wordlist but you would've employed “addi” for “addict”. BIP39 https://letsbookmarkit.com/story18818535/5-simple-techniques-for-bip39-word-list-pdf