For words that have only 3 letters, there isn't a 4th letter. Such as with the word “insert”, there aren't any extra letters afterwards and so has to be the word "add". The word “addict” is while in the BIP39 wordlist but you would've utilised “addi” for “addict”. On this https://bookmarkingquest.com/story19543533/examine-this-report-on-bip39-passphrase