For words that only have three letters, there is not any 4th letter. For instance with the word “include”, there isn't any additional letters afterwards and thus need to be the word "insert". The word “addict” is while in the BIP39 wordlist however you would have made use of “addi” https://friendlybookmark.com/story19369406/the-5-second-trick-for-ledger-seed-phrase-bip39