Technical Rear fender ID needed

Anyone help id this rear fender? I have a pair and they are pretty nice just not sure what they are for!

 

That has got to be NOS.

I'd say it is a sedan fender based on where the bolt holes are. I've never seen a fender that wasted that much sheetmetal under the sedan body.

I say NOS, because if it had been installed, surely it would have rusted where the metal was doubles under the body. Except, it almost looks like there is a line where the paint is faded as it if was on a car?

Would an aftermarket manufacturer make a one-size-fits-all, replacement for a coupe or sedan fender, and then just punch holes as required?

 

I'm gonna go with 1931 Pontiac or other GM product as much as the fender is hidden under the body....

 

Based on the shape at the rear of the fender I would say it is a GM product. 31 or later