The highway 1's were something different - I believe an Acrylic lacquer and not the same as the nitrocellulose thin skins.
I have a Highway-1 body (honey blond transparent) that I am using for a partsocaster project. Having sanded it down in areas and attempting weather checking on it, I believe 100% that there is a poly sealer under the satin nitro. The nitro EVER SO SLIGHTLY checked, but you could see the cracks floating on top of a sealer coat that was completely unaffected by the severe temp changes.
The poly didn't seem to be too thick, though. It sanded off pretty easily.
From what I have read on similar threads, it sounds like only the Thin Skins are actually poly-free. By most reports, Nitro takes a lot longer and apparently Fender doesn't have time in their production schedule to even do any Thin Skins this year. Sorry I don't have the links accessible to reference all of this info at the moment.
OK so MOST Nitro finishes have a Poly undercoat, right?
My Hwy1 has Poly underneath and a thin coat of Nitro. ??