I haven't seen anybody post anything about Baofeng, or clone company, production procedures so I don't know if they calibrate every single radio. I think probably not because that would increase the cost but I could be wrong.
Calibration settings could be determined in a prototype "golden unit" and then the exact same settings could be programmed into the one-time-programmable firmware memory in each production unit.
The UV-5R/UV-82 series have only two trimmers on the board, reference oscillator frequency and power level. I bet that is they only things they set on the production line.
I have never hear of anybody having one with a working S-meter so I don't think that is calibrated at all.
Tom ND5Y
Don't know about these radios but many have oscillator frequencies, RF and IF gain, oscillator injection levels, s-meter calibration and much more saved in software at calibration time so no two radio's images are alike.