It is based on only historical data, by definition. It cannot be 'outdated and unreliable' (due to future expectations), because that's not how it's defined.

It is based on only historical data, by definition. It cannot be 'outdated and unreliable' (due to future expectations), because that's not how it's defined. And it's not how engineering design processes work. (Google LRFD or ASD) 'Now' means the historical data that is current as of design. You are merely setting a design criteria benchmark. Based on historical data. If you want to account for future uncertainty, it goes into the other side of the design equations, via the factors and probabilities. But more fundamentally, picking a 1/500 design storm already takes into account certain aspects of risk levels, and has nothing to do with expected lifetime or survivability. You can and do often pick design storm intervals that greatly exceed design-lifetime, for various reasons.