I encountered this very question just a few short months ago when starting my seeds. Curious myself, I planted a variety of seeds that were all stored the same (on an open shelf, in a brown paper bag, in sealed individual sandwich Ziploc bags, in their original packets) but represented a 4-year spread of expiration dates. I had around a 95% success rate with the seeds dated 2024, around 75% success with 2023 seeds, but only around a 30% success rate with seeds dated 2022 and before. I even had 2 separate packets of herb seeds (dated 2022) that had a staggering 0% success rate. Those were chives and cilantro FYI.
That being said, I definitely saw a significant decrease in germination rate as the seeds got older. I also noticed that the older the seeds were, the more likely they were to become stunted. I had a lot of the 2+ year old seeds that just never progressed through the seedling stage into a starter. Even potting them up did very little to encourage growth. Perhaps if my storage techniques were better there could have been different results. Or maybe it truly is just the age. Who knows.