For words that only have 3 letters, there is not any 4th letter. One example is with the word “include”, there isn't any additional letters afterwards and so has to be the word "add". The word “addict” is while in the BIP39 wordlist however you might have utilized “addi” for https://thebookmarkking.com/story18872058/bip39-phrase-generator-can-be-fun-for-anyone