For words that have only 3 letters, there isn't any 4th letter. For example with the word “insert”, there aren't any extra letters afterwards and thus need to be the word "incorporate". The word “addict” is in the BIP39 wordlist however you would've employed “addi” for “addict”. You signed in https://agendabookmarks.com/story18876831/the-2-minute-rule-for-bip39-all-words