Not all, but perhaps on some. The coating on the factory headlights on one of my other vehicles began to flake off. They were replaced under warranty because of it.

 

I have yet to see a factory UV layer flake off a car. They normally wear down slowly. Anytime you see a lens that has flakes coming off of it that's not the UV layer, thats a sealer, usually polyurethane or acrylic based.
That can happen if the lens is not properly cleaned before the sealer is applied.
There is no sealer applied to the headlights at the factory. The UV layer is bonded to the surface of the lens and it is micro thin. Sanding and polishing is the only thing that would cause the UV layer to flake and even then it would flake off in very small particles like dust.

 

stupid spamsucker!

 

Two things. First, just because you have yet to see it, doesn't mean it doesn't happen. Second thing you said: the UV layer doesn't flake off; it's a sealant. BUT, they do not apply a sealant at the factory. Can you please explain how the original, factory headlights had a sealant flake off that was never there? The UV layer is what goes on the outside of the lens to keep it from degrading. What else would it be? That's why wetsanding is a last resort to restore plastic headlights. It completely removes that layer.

 

Actually what I am saying is that, it is ONLY the sealer that peels off.
The UV layer is not a sealer, It is bonded on the the lens for the purpose of UV protection. UV or Ultra Violet rays will turn plastic yellow.
Being bonded it cannot peal or flake off, the bond is a permanent attachment.
It can be polished off or sanded off, This will take plastic from the lens surface in the process.
A sealer is a DIY treatment that us used as a BAND AID after any abrasive operation.
These sealers are necessary bacause without them you could never get the lens to look smooth or clear after an abrasive cleaning.
It is quite easy for a trained eye to decern the differance from, UV damage, Surface Damage, and Oxidation.

There is only one solution which works best for each problem.
1. UV damage: There is no fix when the lens yellows from UV exposure the lens must be replaced.

2. Surface damage, This can be addressed with a polish, normally most surface damage you see on a headlight is self or user inflicted.
Driving a car cannot create the damage to a plastic lens one abrasive cleaning can.

3. Oxidation, This is removed with a pure liquid non abrasive deoxidizer. There is no damage and the lens can be restored to it's original condition.

Different problems need different solutions and if you don't address that, It will be reflected in your end results.

 

If the factory does not apply a sealer though, what peeled off of my lenses?

 

That was the factory coating. Contrary to what some believe, *******ly all modern factory headlights have a coating to protect the plastic beneath it.

Usually the coating simply oxidizes, but sometimes it gets so bad it delaminates and peels -- especially if they are laid on too thick or not cured properly. There are quality control standards, and production changes, and differences among manufacturers, and so you see a little bit of everything.

 

That is the impression I was under. Thanks!!