The 1983 No mint mark Copper Plated zinc Cent is not an error. The plating was compromised and the inner zinc is starting to rot The 1983 D has Plating bubbles and linear plating blisters. Minor issue. The 1993 looks like harsh chemicals affected the copper plating. It erroded the plating away. Sort of what occured with your nail polish.
No errors. Coins are now zinc and coated with a thin layer of copper. Zinc is a terrible metal for coins. It rots easily. It's very common to find them in circulation that have not been coated correctly.
You can call your 1993-D coin an error, But not a mint error as the planchets used for this coin comes from a private company contractor. As an error coin it only has an appeal to a small % of collectors, those that like F.I.D.O. (freaks, irregular, die breaks & oddities) Coins. Its value is minimal at best. I also suspect it to be Post mint damage.
