They have almost certainly been diluted. They don't do their pro-rata generally on each funding round and my bet is that the YC Continuity Fund was only allowed

They have almost certainly been diluted. They don't do their pro-rata generally on each funding round and my bet is that the YC Continuity Fund was only allowed to do their pro-rata. When the Dropbox S-1 drops we will see what kind of ownership they end up with over time.