Many of the tests provided by the government have had their expiration dates extended as data on usefulness is accumulated over time. See link below for dates. Unfortunately, the ones I got have not had the date extended.
Expiration dates and more about authorized at-home OTC COVID-19 diagnostic tests information.
www.fda.gov
I work for a company that makes similar medical test kits (note: none of our tests are Covid related). For new products, it is quite hard to determine when they will expire. We base our expiration dates on accelerated aging at elevated temperatures, expectations from similar products, manufacturer claims from the individual components, and
business-related reasons. That last part is the most dubious. We don't want to have to recall anything, so we are quite cautious with expiration dates. Basically, if one of these brand new kits says it expires in June, it is probably good for a couple months past that just to avoid the possibility of a recall.
Once more data comes in with stability tests for longer periods of time at different temperatures, then we get real data and put real expiration dates on the products. Often they are far less conservative with the second batch. It is common for us to initially put 6 month dating on kits when later we find out they last 2+ years.