Does Coca-Cola produce its "second tier" products in batches?

I love Coke Zero. My wife loves Diet Coke with Lime. We’ve noticed that at times, both of these are nowhere to be found. All the stores still carry the primary Coke products (Coke Classic/Diet Coke), but not our favorites. We’ve especially noticed it since moving to Maryland. Are these shortages due to freak surges in demand, or does Coca-Cola not produce a continuous supply?