For words that only have three letters, there isn't any 4th letter. For instance with the word “add”, there won't be any more letters Later on and so needs to be the word "insert". The word “addict” is within the BIP39 wordlist but you would've made use of “addi” for https://dftsocial.com/story19785846/helping-the-others-realize-the-advantages-of-bip39-seed-phrase-mnemonics-generator