If you login to your Google AdSense account and go to your AdSense for Search reports, you should see a new warning from Google that they will be deleting AdSense for Search top query data that is older than one year.
The message reads:
Effective December 10, AdSense for Search top query data that's more than a year old will no longer be available. If you have any critical reports, please run and save them prior to December 10.
If you want that data for historical tracking purposes, I would login today and download that data as soon as possible before Google takes it away.
I don't blame Google for deleting it. They can't store data forever. Actually, as I write this, Google is well-known for wanting to store data forever. So why not keep it? They must have some technical reason for wanting to trash old data.
In any event, this is happening on December 10th, so login now and back up that old data.
Forum discussion at WebmasterWorld.