when getting a windscreen replaced, how does one determine whether calibration of safety systems has been done properly, other than relying on what the technician says ?

Don’t sign their job completed receipt until they show you the calibration certificate (or at least something that shows it has been done, eg printout from calibration process)

 

Remember these need to be done in a workshop with appropriate test equipment, so can’t be done by a fitter in a van.