Simple test on how to tell an original sheet vs. a reproduction sheet.
You will need an original sheet (or fragment) for this, a reproduction sheet & two drops of water.
In the example shown, the original fragment is from my 1970 Coronet & the full sheet is one Dave provided to me. (Thanks Dave!) Note how after a few seconds the water drop soaked into the one provided by Dave but it stays on top of the original.
I tried this with several original sheets with the same results.