For words that only have 3 letters, there isn't any 4th letter. Such as with the word “insert”, there aren't any extra letters Later on and thus need to be the word "increase". The word “addict” is while in the BIP39 wordlist however , you would have used “addi” for https://hubwebsites.com/story20116056/the-definitive-guide-to-bip39-seed-phrase