There was no P mint mark in those days. I would recommend taking the coin to a local coin expert or two for an evaluation. The coin would be worth from $50 up to possibly $1000 based upon your description of the wear, but the "P" might actually decrease the value of the coin. There is an error known as a clashed die error where the two dies become damaged by smashing together with no planchet between them, and subsequent coins have the image of the damaged dies. This does not really sound like what has happened in your case, but it is possible. Again, a local coin expert or two would be your best help, or you might post a photo here. I hope that helps.