Everything entered into a database under a vehicle's VIN stays in that database; is that info available to CarFax, for example? This is an example where if you try to sell your car in the future - would that comment show up somewhere? I dunno.
I would go back to the dealer, tell them that "needed repairs" is an completely untrue statement and demand that they purge it from your car's record, and I'd keep escalating it up the chain of command until I got satisfaction. It's the principle of the whole thing - yeah, I also joust with windmills.
I'm afraid I'd get belligerent enough (depending on how many cups of coffee I just had) to have them tell me specifically what the pass/fail criteria are for this 'annual battery calibration check' and why that matters? I'm curious if they bring up battery capacity and thus what the criteria would be for battery replacement.
I doubt that Mitsu would use this in the future if for some reason your battery became defective, but who knows what new management might decide?
If you have EVBatMon it will give you a capacity number for your pack, and CaniOn nicely shows you how well the cells are balanced.
Hmmm, maybe the dealership would like your pack to 'fail' so they can get reimbursed from Mitsubishi for the warranty replacement?
Sad example of upselling, I'm afraid.