Just received two lower rear quarters from my usual. (One was conveniently pre rusted saving me the work of doing it the old fashioned way)
I was assured these would be MR panels but, I see no indication. Don’t the MR panels usually have a little MR tag pasted to them? Or don’t they do that any more?
The ones I have recently acquired did have the sticker (applied with some space age adhesive that you almost have to grind off)
The ones I received last winter from SNG also had the MR sticker. They did not fit as effortlessly as the MR floors and inner sills and required a bit of massaging. Test fit the ones you got and if they fit reasonably well and are heavy sheet metal use them. If the fit is horrible or they are thin sheet metal pursue it with the supplier. There is sheet metal being produced by other manufacturers but I have no experience with it.
these had an SNG sticker. It looked like that a small sticker had been removed and theirs applied over it. But-whew- they seem to fit ok, a tap here, a tap there. The welder is satisfied so I am too.