For words that only have three letters, there is absolutely no 4th letter. For example with the word “add”, there isn't any a lot more letters afterwards and therefore has to be the word "include". The word “addict” is in the BIP39 wordlist however , you would've applied “addi” for https://wisesocialsmedia.com/story4906958/bip39-phrase-generator-can-be-fun-for-anyone