"but at the end of the day you *do* need to have a meter that's within calibration"
Not entirely.
Supply companies have always been content to let 'dumb' meters stay in place almost indefinitely, when it suited their interests. Replacement usually happened if the meter demonstrably stopped working correctly, or on a 'when we get around to it' basis.
I got a "Your meter is out of calibration so we must..." letter from Octopus a couple of years ago. I ignored it and there has been no follow up.