Ok, Vincent, here's my reasoning for why they are still good.
A. They are made of plastic which we know will last a long time.
2. Hotdogs, not made of plastic, will last for years
C. So, if non-plastic hotdogs will last for years then there is no way that those strips should Not work.
Actually, there is an expiration date, but like all man-made devices with expiration dates, they post the absolute low end date so they (the Company) will be held less liable if anything goes wrong.
If the strips were sealed and not exposed to extreme conditions I would still use them. Just check the results against newer ones if your readings with the expired ones are not in the range you expect.