For words that have only 3 letters, there's no 4th letter. For example with the word “insert”, there aren't any more letters Later on and thus need to be the word "incorporate". The word “addict” is in the BIP39 wordlist however, you would have utilised “addi” for “addict”. A seed https://linkingbookmark.com/story18803059/considerations-to-know-about-bip39-word-list-pdf