Once the human race has extinguished itself, it will take Mother Nature approximately 10,000 years to eviscerate all signs of human endeavor (save for all things nuclear and, well, Cher). Based upon that, all remaining "pins" would likely biodegrade within about 2,000 years.
This. If you can afford drugs you can afford pins.
And to answer to the question, I have no idea. Never tracked time on these. As longs as the package has been sealed and stored properly you should be just fine.