If I'm following this correctly, this will select all pending exists with an audit period less than the max.
So, let's say for some reason the verifier is down for an entire day and we end up with two day's worth
of exists in pending status. This will select and verify two sets of daily exists. But, when the _verify
function above will only return exists[0] to the callback. Thus, the callback will only emit the notification
for one exists when really it verified two. This is a pretty critical bug, unless my understanding of this is
incorrect.