Robert_Charlton - 5:42 am on May 21, 2013 (gmt 0)
Does this have something to do with the latest update rumblings?
Hmmm... thinking out loud, and guessing....
This most likely means that Google is running an old dataset, possibly among other datasets, perhaps for purposes of comparison. This seems to happen at times of big change.
It's hard to know how broadly sites are being affected, so I hesitate to whip out a crystal ball, but "2 years ago" sounds bigger than, say, 'six months ago' might.
How have you been doing in updates over the past several years? Mayday? Panda? Penguin? This might suggest how big a swath could be noticeably affected.