That's a reasonable explanation but not quite what I was curious about. Not renewing a warrant if further evidence is missing is a good step but I'm wondering i

That's a reasonable explanation but not quite what I was curious about. Not renewing a warrant if further evidence is missing is a good step but I'm wondering if the proportion of warrants that turn up nothing after all is not a better measure for whether the system is used for abuse. If overall the system has a low "false positive" ratio, especially among journalists, then it's hard to argue that it's abused. But if it turns out most of the warrants (or something that stands out) issued on journalists end up bringing irrelevant info then it could raise suspicions.