This question has an interesting property, in that judging a winner is dependent on unknown data:
This is actually not an uncommon way of things working in puzzle-space. In programming competitions, you often are given simple test data and then you submit your program to a server where it is run against some kind of pathological data which you are not given in advance.
But if a winner is to be declared, there is a question of when and how that data will be disclosed. It introduces a factor of timing into it such that no entry can be accepted after the revelation point.
Does such a question with an undisclosed winning condition deserve its own tag? Should there be a rule that once a winner is declared, the test data be published, and no answers accepted after that point?