I would draw one conclusion - Google does not put their public reporting operators on a very high level of importance, compared to all the other things they do. One possible reason: they don't want to enable intensive competitive research.
Google is doing a better job with the private WebmasterTools data, at least a good bit of the time. That reporting is behind a log-in, where only the validated site owner can have (or intentionally share) access. Safely tucked away from your competitors and malicious intentions.
However, even Webmaster Tools reporting gets buggy when Google makes significant changes to their back-end infrastructure (which seems to have happened this month).
I think this particular bug is fascinating - it might even tell us something about Google's back-end data storage. But, we have so little detail about that - it's almost impossible to extrapolate a useful insight as it stands.
Ny guess would be that a chunk of information became inaccessible to the site: operator when they changed something on the backend. It's even possible that a chunk of data went missing while they were moving it around between data centers - that's happened before. What KIND of data that is would be interesting to know, but I can only make wild guesses, so I won't.