Grips for decocker and non decocker are not interchangeable. The top screw holes in the left grips are in different locations. Here is a picture of a set of Hogue grips...the non decocker grip for the left side is in the middle while the decocker version is on the left. Note the difference in location between the top screw holes.
Welcome aboard, Jim, and congratulations on your purchase of a fine firearm. Your pistol is considered to be a "pre-decocker" gun. As CWB noted above, the grips are not interchangeable between decocker and non decocker guns, so keep that in mind if you decide to get an extra set of aftermarket grips. Enjoy your PT 99.