[BillyCoxDodgers3B]

My question is if it was more a case of being stored in a humid environment rather than the fault of the holder.

I have discovered boxes upon boxes of cards in top loaders from my youth that have all turned that fetching shade of nicotine. All were kept in an ideal, unchanging clime for decades, and all were fine. The top loaders looked like a disaster, but the cards, once removed, were as bright and beautiful as a tranquil sunrise. And, because they were from my youth, this predated when the 1-2 punch of the penny sleeve/top loader came into play. These cards were naked inside their top loaders, so had been exposed to over 30 years of direct contact with the plastic.

In fact, just yesterday, I discovered a stack of goodies that had sat in a corner, forgotten about since the days when you could say "Bel Biv Devoe" and people didn't immediately think you were having a grand mal seizure. A small pile of 52T, and for my fellow hockey lovers, a pair of Turk Broda rookies. Nicotine top loaders. All was well.

Then again, the OP was using some sort of off-brand Card Saver, and I'm going on about top loaders. Perhaps my musings amount to apples vs. oranges because of this? Who knows.