you look at the edge of the coin. Genuine 1943 Zinc coated steel cents were not zinc plated on the edges. If the coin's obverse and reverse sides match the finish on the edge, it's been re-plated
1- NO cents have ever had a P mintmark till 2017, and --according to the mint-- the last year. So a P/S would be impossible. 2- What you are seeing is a die break in the mintmark. Pretty common coins from the 70s and 80s, especially nickels.
Cherry Picked these at the local Flea Market this morning. He had them marked for $3.50 but I Got them all for $22. He had about 60 of these P,D,S sets. Each set has an rpm so I figured I did pretty good. And the 1837 I purchased simply because I've never owned anything this old. Very Satisfied Here.
I have a MS-67 that became corroded in a PCGS slab. PCGS said the slabs are water resistant but not water proof. I said, what about humidity? We live in Hawaii and humidity shouldn't be an issue. And why only this one coin? I'm guessing it was a bad slabbing that PCGS denies.