The notion of trusting Google becomes more and more unlikely. I've been using the Alert service since December 2011 to monitor the news on e-books, in the expectation that we might get some funding for research on the subject. However,when I started to analyse the data recently, I discovered that there appears to be a maximum count of 45 items in any one Alert - in fact in 36 out of 59 days examined so far this was the case - and no day exceeded 45 items.
Using the service to try to discover trends in news reporting, therefore, is made impossible, since one will never know the "true" number of items published, or even discovered by Google's spiders. As far as I can discover, there is no information on the Alerts site about any such limitation. When one couples this problem with the further difficulty that Google covers much more of the US news than anywhere else in the world it become difficult to treat the service seriously.