Lots of things in life have expiration dates. Food and drink items that you buy at the grocery store, for example. The expiration date is printed right on the side of that carton of milk in the back of your fridge. You don't even have to take a sniff to know whether it's still good. (Once in a while, of course, you should probably still take a sniff anyway.) Can't remember when you bought those hot dogs in the cheese drawer? Just check the package.
Food and drink and other perishables, of course, will go bad whether or not you remember to check the date. Sometime you leave some bread on the counter too long and those telltale green and white spots starts to appear. Even if you diligently "refrigerate after opening," food and drink that sits too long goes bad in spite of proper temperature control. When it comes to groceries, the expiration date is a gentle reminder, not a guarantee.
In other walks of life, expiration dates are more arbitrarily chosen. You may not be permitted to buy things with an old credit card, for example, but it's not as if the card itself will melt into goo on the last day of December 2022 (or whenever it is). Or take certification exams. Say that you passed the 900 series of exams to become A+ certified by CompTIA. Most of what you learned will probably still apply after July 31 of this year.
That's still an important date, however, because after July 31 (or Oct. 1, for non-English-language test takers), the 901 and 902 exams will no longer be available. If you want to get your A+ certification after that, then you will need to pass the 1000 series exams. And those exams, being newer, have different content. If you've only studied using materials that reflect the 900 series content, then you'll have gaps in your knowledge.
TestOut has you covered. The new A+ exam was released on January 1. Our new A+ training was released the next day. We don't cut corners with keeping our courseware current. When CompTIA released the new single-exam Linux+ on April 2, our new Linux+ training was available on April 3. We can't really help with that forgotten brick of sharp cheddar — although some people say a little mold makes cheese taste better — but our training is always fresh as a daisy.