Bill says "even with the lamination like mark." because he's thinking the same thing I'm thinking.
This coin is a white elephant...it's a key date coin with a minor error. On any other coin the minor error would be an addition to the coin, but with a key date coin, the minor errors often get in the way of selling the coin at full value, and in some cases, being able to find a buyer for the coin at all. Many people want a 'problem free' key date coin, meaning a coin that has no errors or other flaws. A lot of people see these minor mint caused errors in the same light as coin damage.
As for me personally, if I were to buy a 1909S cent I wouldn't want mine to have the lamination, but that's just me.
Anyhow, not to rain on a parade, this is a very super find for the price, and is still a nice, valuable piece.
I see no problem with authenticity.