That's the copyright/design year of the part. It's common for Apple to not change some parts in their machines as they upgrade them. An example is the Magsafe board on the 13" Macbook Pros. They are all the exact same from 2009 through 2012 and all say 2009 on them, just like your board does.
This is normal, the 2009 4,1 mac pro and the 2010-2012 5,1 are mechanically the same computer. Just different firmwares and accessories like vid cards, drives, cpu's, ram.