For words that only have three letters, there isn't a 4th letter. As an example with the word “insert”, there won't be any extra letters Later on and thus needs to be the word "insert". The word “addict” is during the BIP39 wordlist however you might have used “addi” for https://7bookmarks.com/story18702043/the-fact-about-valid-bip39-seed-phrase-that-no-one-is-suggesting