I am not sure that is correct. I listened to Tom Boyd who is the VP of Simulations at Cruise. There are 2 kinds of simulations. There is replay which is what you are talking about, where you just replay existing events to the car. But there are simulations that you build, a lot like making a computer game simulation. You can build new scenarios in those.
Here is what Cruise's 3D simulations look like. I believe they can add new scenarios to these simulations.
To be clear, I am not suggesting that you don't need any real-world data or real-world testing. Of course you do. Simulations do not replace real world data. But I do believe it is possible to generate new scenarios in simulations.