No need to assume any of that! If the camera module had storage, calibration data could be stored on the module itself, whenever the calibration is done. Would it be more expensive? Marginally, but yes, definitely. But that's not the point of the discussion. The point is: did Apple decide to make cameras not exchangeable because of calibration data? That could be considered a poor choice from the point of view of the customer: they shave a couple dollars from memory, but you get less repairability. It's not the trade-off I would want to see.
Again, because we now seem to live in a world where thinking things through a bit sends folks off into a fit of pique, I'll start by saying I'm not sure how the calibration works for iPhone 12 or why Apple is further restricting who can service camera, but let me think this through another step.
Apple ships something like 200 million iPhones a year. How many have camera repairs done on them? Is it worth adding the cost of the components to every device that ships just to make it easier for unauthorized 3rd party repair of the much smaller number that need the camera replaced when when you already have plenty of space to store that data right where it's being used on the processor side of the connector?
Every component added is another potential point of failure, so is it worth increasing the overall failure rate just to make it easier for 3rd party repair?
Space is tight inside the phone, and every cubic mm is fought for. What features should be sacrificed to add the storage making it easier for 3rd party repair of the small number of phones that require camera repair?
I don't think the accelerometers and gyros are in the camera module, so even if the camera module itself were factory calibrated, there's another set of extrinsics that may still need to be done for motion tracking.
And then, as the module is installed (which has tolerances to account for) and ages, the calibrations can be expected to shift. So a precalibration may not be sufficient, and may require special equipment that certified techs are known to have but other 3rd parties may not so the software check-in may just be a way of ensuring that the calibration is done at all.
I don't know how or if calibrations are done by repair techs, but my point is just that the camera isn't a battery or a screen, it's part of a remarkable computational photography, motion tracking and augmented reality engine and improvement are increasingly dependent on those sensors working well together.
I'm not sure Apple would choose to give up any small amount of performance in every unit shipped to make it easier to repair whatever small fraction are brought back to unauthorized repair shops specifically for camera repairs. I'm also not sure that the economics work in the customers favor if they did.
So why then pretty much the same 2x/3x cameras on previous models, capable of the same computational & HDR10 / night mode tricks do not require kinda authorization?
Yeah, that's part of what gives me pause. The Pro/nonPro modules are pretty similar though, and the computational photography algorithms have evolved a bit, so it's possible they changed their calibration strategy between last generation and this or just decided to follow the same procedure for the non-Pro that they found they needed for the Pro. Or maybe they discovered that the repairs weren't being handled correctly with the 11 and wanted to ensure fewer user complaints in the 12.
Or maybe calibration has nothing to do with it. I was just thinking about what might lead to special treatment of the camera and that was one thing that came to mind.