Comment by alamsterdam

Yes, I was wondering what is to stop you replaying the same PoW multiple times. All I can find is:

To prevent the vulnerability of “replay attacks,” where a client resubmits the same solution multiple times, the server should implement measures that invalidate previously solved challenges.

The server should maintain a registry of solved challenges and reject any submissions that attempt to reuse a challenge that has already been successfully solved.

This doesn't seem very scaleable? Or am I missing something?