Do black & milds get old/stale?!
They won't be as fresh as if you just bought the pack, but they should be fine, its not like they were sitting out in the open. Think of it like a box of cereal. If you leave it open, it gets stale. If you keep it sealed, it's fine.
All tobacco will react to moisture from the air, but this pack ought to be okay....if it is not, don't pitch the tobacco, save it in a jar for bee-stings!!
They may be a little more dried out than you'd like so they'll burn faster and be a little harsher but they won't kill you-well, you know what I mean.
In some stores I bet they sit on the shelf that long.