I have only discovered a few pieces, so far. When I get to the bottom of this box, I bet there will only be about 5 or 6 pieces of the stuff 4x6 inches in size.
Not enough to cause an international incident but, as with all things, due caution is advised. They've been around for 50 years without incident and they show only the most minimal deterioration, if any at all. If stored safely, there should be no problem.
I have a metal box to store them in and I will keep it segregated from everything else until I decide what to do.