July 14, 2017, 8:21 p.m. PDT
Thanks for the prompt response and helpful explanation!
In case you're curious, I wasn't referring to nonmonetary prizes, but to contests where prizes are advertised but then not awarded. In some cases, the explanation is that even the top winner failed to cross a minimum performance bar identified in the challenge description, but in other cases it seems to be just to save money. For example, the Abundant Clean Energy contest advertised a purse of $50K in five $10K prizes for ideas on structuring an XPRIZE (https://herox.com/AbundantCleanEnergy
) plus a $10K wiki quick start prize (https://herox.com/AbundantCleanEnergyQuickStartWikiPrize
), but then only two submissions were actually selected to receive awards, and the limit wasn't due to the absences of valuable submissions (28 >> 2). That sends a signal to solvers that prizes posted & hosted here aren't all actually real.
With the NatGeo challenge being externally hosted and just promoted here, and the helpful "People's Choice" explanation, that does give greater confidence that "all prizes...will be awarded." Thanks for clarifying!