I think that one came out before I bought my router...the Asus download site says 2012.02.02 (Feb. 2, 2012), so I wouldn't have tried it. Think that I started with a later firmware than that one, since I got my rt-n66u router at the end of March, 2012, as I recall.
Are you thinking that it's newer because of the "3.1" part? It's actually really old.