Yes, it’s been around that long. Diet Coke first hit store shelves back in 1982. Long-suffering dieters, sick of saccharine colas with aftertaste that lingered for weeks, embraced the aspartame-sweetened brew—and it’s been the No. 1 seller in its category ever since. But while keeping the 29-year-old formula is de rigueur, a can design from the Reagan era is a bit less plausible.