For words that only have 3 letters, there isn't a 4th letter. Such as with the word “insert”, there are no far more letters afterwards and thus need to be the word "include". The word “addict” is in the BIP39 wordlist however , you might have used “addi” for “addict”. https://myfirstbookmark.com/story19634249/facts-about-bip39-seed-phrase-word-list-revealed