The staples under a cheekpiece would be for a steel vent pick. If you have "Rifles of Colonial America, vol. 2", look at gun number 111. There is a nifty little pick clipped into the staples. My belief is that this was the more common use of the staples (rather than for a feather). You will also sometimes (though not very often) see a hole in the rear of the cheekpiece, sometimes even with a threaded insert, where the pick will be inserted into the stock. Sometimes a threaded inlay on the bottom of the stock behind the triggerguard would hold a threaded vent pick.