Systems which can't update their libc or other system software have already broken in various ways. For example, in 2007 the Energy Policy Act of 2005 changed the date when DST begins and ends. Any system unable to update its libc data files since about 13-15 years ago will display the incorrect time. I have a cheap $10 radio clock which I've had for two decades. It always displays the wrong time for a few weeks around the DST change.

Any system which needs to display the correct time needs to have a mechanism for updates.

The time_t wraparound is a bit deeper and more serious, granted.