I haven't bought the latest, 5th Edition of the Standard Catalog of the Smith & Wesson, the 4th which I have, only seems to go up till 2015. I could find no Ps in any prefix that's listed here. Perhaps that's why you asked the question. There are some guys here who seem to keep personal records (For their private reasons I suppose) of the Triple Alpha Ser. numbers who may come across this thread and help you more than me.
Welcome to the Forum, by the way! In case you don't know, up at the top-middle of the home page, if you have the spare bucks, maybe pick a level you're comfortable with and become a contributing member. The ads on the sides will magically disappear!
Also, a picture of the gun is always helpful. If you have the original box, the end label should have the date of manufacture on it. S&W goes by the Shipping-from-the-factory date on it as its date.
You may want to introduce yourself in the New Members sub forum. Maybe add an approximate location of where you hail from.
Jeff T., Pittsburgh, PA