For words that have only three letters, there isn't a 4th letter. By way of example with the word “include”, there won't be any much more letters afterwards and thus have to be the word "include". The word “addict” is within the BIP39 wordlist however you might have applied “addi” https://yesbookmarks.com/story18927862/new-step-by-step-map-for-bip39-english-words