Here’s a commentary from the Mayo Clinic on the shelf life (and expiration dates) of medications. It seems that the expiration dates on your drugs are only the dates to which the manufacturer guarantees full potency, but they’re only, by law, required to guarantee it for three years for approval by the FDA, so none of them bother to test for longer durations. While some drugs do break down soon after the “best by” date (aspirin being a notable example), a study found that some were still useful some 20 years after their marked expiration date.
https://www.mayoclinicproceedings.org/article/S0025-6196(15)00667-9/fulltext
https://www.mayoclinicproceedings.org/article/S0025-6196(15)00667-9/fulltext