Original early CharlieCards were programmed to expire in 5 years. Apparently at the time, the belief was the cards wouldn't physically last much longer, so the idea was to force people to transfer their balances to new cards prior to the point when the cards failed.
As the 5 year deadline approached, they realized the cards would last longer, so if you did an "upgrade" at a fare vending machine, you got another 5 years added to the expiration. There was a limited window where this reprogramming was available, so by no any original cards w/o this patch won't work. The CharlieCard store may or may not be able to recover a balance off the card.
Newer cards are printed with an expiration date on the front. I believe these started with dates in 2021 and later.
That said, the T is working on AFC (Automated Fare Collection) 2.0 which will be a radical departure from the current CharlieSystem. It's quite likely the existing cards will not work with the new system, which will be fully account-based (i.e., no balance info lives on the card). No official word on when it will debut, but the T seems to be moving the project along at a good clip.