It will depend on the card and how it's stored.
Stuff like T206s are on cardstock that's probably pretty close to acid free. The same for most other T cards and caramel cards around 1910 ish.
Unless they're stored very poorly they should be fine for a long time.
Stuff like strip cards are on poor quality cardstock with a lot of wood fibers. That stuff eventually breaks down and releases acidic vapors that will accelerate that breakdown. Again, it varies with different storage.
SGC cases are not airtight, which is ok because those gasses can get out of the slab. I'd have to do some experiments to see about how quickly the air inside vents and new air comes in, but from what I've seen of all slabs it probably cycles through quickly enough to be fine.
UV protection depends on what plastic the slabs are. Polycarbonate -Lexan has some UV blocking properties. I don't recall seeing any technical specs on the slabs themselves, but polycarbonate would be a pretty good choice for durability and clarity.
Steve B
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