[klausa]

Why would the calibration details need to account for all iPads sold?

Just bake the one that the device is bonded with, using the display serial number as a lookup key.

Then, if you change the serial number of the display, the lookup would fail, and fall back to whatever "default" values are.

[rasz]

and just be shear coincident two screens, the broken one and replacement, match calibration data completely?

[Too]

Actually not that unlikely, imagine the allowed range of calibration is 0-100, the factory is likely to produce parts with small variance, but having same constant offset, resulting in output of screens between 70-80. While default in software might be set exactly in the middle at 50. Knowing how a large organization works, the default set in sw is probably not even close to what comes out of production lines, it's just an assumption some dev made that happened to work good enough on his desk 4 years ago.

Even if the screens would cover the whole spectrum, there is still a high chance this coincidence could happen, and more data would be needed to validate either theory. Is there any statistics showing that this happens all the time or just some times.