"Confirmed Dead" - the second episode of this season's 'Lost'......
When Frank Lapidus recognized that the body shown on TV (which was supposedly of the pilot of Oceanic Flight 815) was NOT Seth Norris, it was because the body wasn't wearing a wedding ring. It was not because he had no mustache, as shown in his identification photo.
Simple splainin on that - between the time the picture was taken and his final flight, Seth Norris shaved off his mustache.
Behind the scenes reason a mustache was added? I think it's because in the years since he played the ill-fated pilot in the show's pilot episode, Greg Grunberg had become widely known as Matt Parkman, telepathic cop on 'Heroes'. And even though he's best buds with JJ Abrams, the producer of 'Lost', I'm sure the Powers That Be at Bad Robot didn't want the audience at home making that connection.
That's my story and I'm sticking with it.
(Thanks to the "Lost Easter Eggs" blog for the picture)