Is it possible it reversed carbon spot?

I had obtained a High Relief Saint around 2 1/2 Years ago. When I received it I could've sworn there was a carbon spot on the knee. I confirmed it when I dug up the initial photo's I had taken of it. During the last 2 1/2 years this coin was kept in an Intercept Shield Double Row slab storage box at my bank safety deposit box. I recently pulled it out and lo and behold, no carbon spot on the knee! Is it possible the chemical within the intercept shield removed the carbon spot in the span of a couple of years? I'm totally flabbergasted.