Is This A 1909-S ?

I know everyone says not to do this, but if you want to increase your chances of determining this date, I'd clean it with weak acid or even an eraser from the back of a pencil. The coin is already poor (lowest grade), so if cleaning it tells you the date, at least you know- you are not going to lower the grade any further, it is already a PR-1. Of course, you could clean it and it still will be unknown for sure. I've done the eraser method (very light erasing) on a few bad cents and was able to date them after not knowing before cleaning them.

I tried freezing it in water and thawing it a few times. That did nothing. I think I'm done trying to figure it out. It really looks like a 1919 to me, but I finally just put it in the '09 slot for the kids and some day maybe we'll have a real one.