I’ve developed a minor obsession with Google search result listings text. This short, information–rich block of text is surprisingly difficult to control; there’s a lot going on behind the scenes, and Google is vague on how it’s actually generated.
It’s certainly not science. When you start testing Google search queries on your own pages you’ll get some strange results, just like I did when I started using UK date formats and used an about class on a page. Oddly enough, Google also thinks that the Radio 5 home page was last updated in 1971:

The internet did not exist in 1971.
While I understand that knowing when a page was updated allows readers to evaluate how relevant a search result may or may not be, I’m not entirely sure why Google prefixes a date to search result listings text if it can’t read dates with some degree of accuracy.