I have confirmed that my Mercier Kilo TT did, in fact, come stock with a Dura Ace cog. I swapped out my cog again today, hopping up from a 16t to a 17t. Sure enough, stamped on the cog underneath the lockring (right where it is on the other DA cog) are the words "Shimano" on one side and "Dura Ace" on the other.

*shakes head and snickers*

Sheesh.

So now I have two brand new Dura Ace 16t cogs. If anyone needs one, let me know.