How do they know that a coin like this wasn't just eletroplated https://www.ebay.com/itm/274309817901?hash=item3fde23a62d:g:p8kAAOSwL9pecObd
The finish looks different when a coin has been electroplated. It's really easy to tell once you know what to look for.
Here's another trick. The sheets used for 1943 cents were plated before the blanks were punched (unlike the zinc cents which are copper plated after the blank is punched). The entire edge is exposed steel. Depending on the storage conditions, the steel can have a different toning than the zinc plated surfaces. Reprocessed 1943 cents are completely replated including the edges. Not every original coin will exhibit a color difference, but it's another piece of info to keep in your tool bag.
Here are a 1910 Plated and a 1943 Plated. Pulled both from circulation way back when. The 1910 had been in circulation for some time.
Would not the weight be a key variable, too? Is the question how one would know if a 1943 CuSnZn cent was electroplated? Aside from the questionable sanity of doing so, a CuSnZn cent should weigh about 3.11 grams. A Zn clad steel cent should weigh about 2.70 grams. I think that's why the weight of planchet is specified. Or am I way off? Or did the question go right over my head?
yeah, original steel cents, the coining sheets were galvanized with zinc and then punched out so the edges for the most part are bare steel, sort of like how you see the copper on the edge of a dime or quarter. If it was electroplated, the edge will be coated in zinc also, so this is how they know for sure it wasn't electroplated to bring up the weight to 2.9 from 2.7g it's a rolled thick planchet I guess.