It's just a convention. We (moderators) append the year of an article (in parens) when an article is from a previous year. Of course we miss many cases, and commenters often helpfully point those out. In this case colinprince added the year to the title (thanks!) but otherwise we would have.

It's not that anybody did anything wrong—historical material is welcome here! and it's nice for readers to know roughly what time an article dates from. That's all.

Sorry I was snippy, I thought they were casting aspersions on the science inside the article due to the date, which is a pet peeve given anything biosciences related moves much more slowly than CS given the (rightful and good) restrictions around human subjects research.