It is standard practice lately for reviewers to require that at least ten people somewhat local to the cache (including the cache owner) have completed the challenge and that all challenges have a checker, before publication.
For clarity, when the checker says that 64 people have qualified, that means that 64 of the people that have tried the checker have qualified. That doesn't tell you anything about how many people that qualify there are in total. There will almost certainly be people that qualify that haven't tested the checker, and if the checker has been run multiple times for the same username (which doesn't have to belong to the person actually running the checker) I would think they are counted multiple times.