For words that only have 3 letters, there's no 4th letter. For example with the word “add”, there aren't any additional letters Later on and therefore should be the word "insert". The word “addict” is within the BIP39 wordlist but you might have used “addi” for “addict”. Locating just one https://bookmarking1.com/story19020853/not-known-factual-statements-about-bip39-explained