If I plan on storing or not using a gun for awhile I make it a habit to stick on a piece of blue painters tape on the stock that shows fill date, fill pressure after it settles, and time of fill. It sure beats trying to go off of memory if you so happen to unbox the gun and it shows a reading below what you normally fill it to.

Was it that extra shot you took before putting it away? Was your fill tank already too low to top off your gun at the time? A possible leak? 

At 57 years old, I wouldn’t be able to remember, so that’s why I label.