From everything I have seen since day one and, no matter the age of the pieces; water (humidity/moisture) has caused, and is one of the problems you mention (see Thomas C. Day's article at our club website) which could be the reason why there were undamaged pieces in the same carton with the bad pieces... There are also posts here from Europe explaining proper storage.

Regarding what you wrapped in plastic, I made that mistake, too.

Huge finds are left to sleep and passed over by some (me, too) in our hobby... even though a piece or two make their way out and into the hands of a few collectors; of which 20 to 30 years have passed, and some being embedded as paperweights, but most is still in storage and thus far avoided except for a photo of some pieces from some series being submitted to ChipGuide.

Yes. There is danger and caution as mentioned in your recent threads and in the past as well.

I have also seen the damage this stuff has caused when in contact with well-maintained collections and in bank vaults.