For words that have only three letters, there is not any 4th letter. For instance with the word “insert”, there isn't any far more letters afterwards and so needs to be the word "increase". The word “addict” is inside the BIP39 wordlist however, you might have used “addi” for “addict”. https://socialmediainuk.com/story20243700/considerations-to-know-about-bip39-word-list-pdf