For words that only have 3 letters, there isn't any 4th letter. One example is with the word “insert”, there aren't any a lot more letters afterwards and thus has to be the word "include". The word “addict” is within the BIP39 wordlist however you would have used “addi” for https://agendabookmarks.com/story19072688/ledger-seed-phrase-bip39-no-further-a-mystery