Texas,
If you unload and field strip you P9 you will see the formentioned rails on either side of inside of the dust cover.
I recently purchased a used P9 Covert (MK length frame) to keep my early model K9 company.
So far mine is 100%, but I did add a couple of things to make it a bit more user friendly. I first added the Pearce magazine extensions. It allows you to get your pinky on the gun without sacraficing concealment. I also added a Brooks AGrip, now it doesn't shift at all when fired. These two additions made the gun so user friendly, it will probably become my primary warm weather carry gun.