For words that only have 3 letters, there is no 4th letter. One example is with the word “add”, there won't be any a lot more letters afterwards and thus should be the word "add". The word “addict” is during the BIP39 wordlist but you would have used “addi” for https://bookmarklinkz.com/story19403508/5-simple-techniques-for-bip39-seed-phrase