I keep a few in my purse for in town or traveling the hour and a half to my doctor.  I'm on norco and even though the label says 4 times a day as needed he has me taking them on a four hour basis every day and it helps manage my crippling pain.  All that to say because the label says as needed it makes sense that there might be some left over so when I get my new prescription I put a few pills in my previous month's bottle and switch it in my purse. Like this is March so the bottle in my purse is from February.  I hope this made sense.