For words that only have three letters, there isn't a 4th letter. One example is with the word “add”, there are no a lot more letters afterwards and thus has to be the word "insert". The word “addict” is from the BIP39 wordlist but you would have utilised “addi” for https://easiestbookmarks.com/story19555790/a-review-of-bip39-phrase-list