This 1969-D Cent was coated in zinc and is not a steel cent. Many copper cents where coated with zinc, mercury or other metals, and this decreases the value of the coin.
This 2000-P Dime was plated in Gold.
This 1943 Lincoln Steel Cent was plated or coated in copper. You can tell the difference because a true copper cent will not attract a magnet. Sometimes you can look at the edges because sometimes they where not coated, revealing the true color and hopefully metal content.
Plated, Coated or painted coins are damaged coins and have no extra value, and often the plating decreases the value. I would consider all plated, coated or painted coins as face value only, unless it's a key date, albeit a devalued key date at that.