The seed germination rates typically decline about 10% each year they're kept in storage, although this rate can vary depending on the species of grass.
To determine if your seeds are still good, open the container and inspect the seeds closely. Make sure they don’t have a funky odor or look wet or moldy.
If they seem fine, place ten seeds on a damp paper towel in a warm area for ten days. If fewer than five seeds sprout, your seeds likely have less than 50% efficacy.