Caffeine-free diet coke (aka Cantina de San Angel)

Since when has the Cantina de San Angel offered only caffeine-free diet? They have regular coke, but the only diet they have has no caffeine. Has this always been the case?

I ate there this weekend and they have REALLY turned around the food here. We swore off this place 3 years ago but finally tried it again, and man is it better. Rice and refried beans has given way to salsa and black beans, and the difference those make in the burritos, tacos, etc, is hard to overstate. I'd go so far as to call this food delicious, which is really amazing.