But it is an interesting question: What is the manufacturing tolerance? Naively I had assumed that it's much smaller than a watt-hour. But that's based on ~no knowledge :D
It’s a nominal capacity that’s printed on the battery, and encoded into its firmware. In practice, batteries tend to exceed this nominal capacity when they’re brand new which is why you see new batteries stay on 100% charge for a long time. As it ages, the true capacity will degrade and eventually falls below the nominal capacity.
Well it could be that the capacity is 3200-3349, and they publish the number that is in the center of confidence interval. Rounding up would be received badly, and rounding down suggests it has less capacity than it really does (on average)
There would be manufacturing differences that would induce at least some variation from phone-to-phone.