manufacture date on headlight units

[kartone]

Had the front bumper repaired on a Mazda 3.
In daylight the next day there was a very visible difference in the "clearness" of the plastic len between the driver-side and passenger-side front light units.
At this point in time the only reason for the "instant" degradation is that the unit was switched while at the repairer.
Does anyone know if and where on these light units there is a date of manufacture ?