Since its a thing done by the supplier and that the passenger and drivers taillight housings are not specific to one side or the other the markings can be found on both and often still there. The markings have been documented on either side. Often matching on both on a specific car likely due to the fact that they likely came from the same shipment or container from the supplier from the same workers station. Either both left side (looking at the rear of the housing) or both right is pretty typical Have seen a very few where the worker that shift put them below the hole for the bulb but that has not be found very often