For words that only have 3 letters, there isn't any 4th letter. By way of example with the word “insert”, there isn't any a lot more letters afterwards and so have to be the word "include". The word “addict” is inside the BIP39 wordlist however, you would have used “addi” https://7bookmarks.com/story18710964/bip39-phrase-generator-can-be-fun-for-anyone