I would expect that it is still good. I have some that is pretty old and it still shoots but I have a bunch of real black powder so I seldom shoot any of the substitute stuff. I know that Pyrodex will have some deterioration over time and the MV will drop off as it ages. So, if you measured the MV at some time in the past and set your sights accordingly, you will likely have to adjust your sights or your powder charge for any decrease in MV. Still, even with a drop in MV, if you take that into consideration the stuff should work just fine providing it has been stored properly.
Of course, it only works in caplock guns, not in flintlocks. But, I suspect that you know that.