Many of the lost records will go unnoticed for days, or weeks, perhaps even months. They all suffer if the bug bites. And it's all due to that pesky millennium bug. As you likely know by now, the century indicator was left off to conserve space and maintain compatibility with older systems. Programmers, the ones who write the program code, and those who design the application, System Analysts, intentionally ensure that required date fields are present.
Most applications have many date fields.
Take a typical product record for example. It may require the user to enter many dates into the system including expiration date, price effective from and through dates, and numerous other dates. Now you get the picture. Product expiration dates, for example, may be used on perishable items, so that date is required from the user. Those program masters that design the system ensure that a date is entered because from that moment forward, the expiration date will be tested to be certain those products that have expired are removed from inventory and are not sold.