For words that have only 3 letters, there isn't any 4th letter. One example is with the word “add”, there won't be any a lot more letters Later on and therefore has to be the word "increase". The word “addict” is during the BIP39 wordlist however, you would've applied “addi” https://bookmarklinkz.com/story19404357/the-invalid-bip39-phrase-diaries