It would not surprise me if more works have been lost than published.
It depends on how you define published because until around 200 years ago only a few were able to read and write in the first place. They didnt have the 99% literacy of today where everyone at some point has had to write something. Today there are tens of thousands of pieces of new literature written everyday and placed online for all to see. I bet in the ancient world there was not even 1 million people across the world at any one time who could read and write.