After I get the bike back from Rob, perhaps next week, I will look again. As I said in my original post, the frame and fork steerer have the same serial number stamped on: 1492. Frankly I don't expect to find anything different when I look again, though finding traces of a fifth digit would be excellent. But this next time I look I am also going to look inside the head tube. If I see putty-filled rivet holes, then I'll be sure.