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(Links to documents appear after the summary.)
This, in my view, is the biggest unsolvable problem of the y2k challenge. If a company somehow revises its computer systems' legacy code, tests it by parallel testing, does not crash its systems during the testing, and transports all of its old data to the newly compliant system, it faces a problem: it is part of a larger system. Computers transfer data to other computers. If the compliant computer imports data from a noncompliant computer, the noncompliant data will corrupt the compliant system's data. A company may have spent tens of millions on its repair, but once it imports noncompliant data, it has the y2k problem again.
Next, if a compliant computer sends compliant data in a compliant format to another computer, this transfer may crash that computer. Or the recipent computer may not recognize the compliant format. The system breaks down.
A noncompliant compuer's data can corrupt a compliant computer's data. But those in charge of the compliant computer may not recognize this when it happens. They may then allow their supposedly compliant computer to spread the data with others. Like a virus, the bad data will reinfect the system. I describe this dilemma as "reinfection vs. quarantine."
Every organization that operates in an environment of other organizations' computers is part of a larger system. If it imports bad data from other computers in the overall network, the y2k problem reappears. But if it locks out all data from noncompliant sources, it must remove itself from the overall system until that system is compliant. This threatens the survival of the entire system. Only if most of the participants in a system are compliant will the system survive.
Consider banking. A bank that is taken out of the banking system for a month -- possibly a week -- will go bankrupt. But if it imports noncompliant data, it will go bankrupt. A banking system filled with banks that lock out each other is no longer a system.
There is no universally agreed-upon y2k compliance standard. There is also no sovereign authority possessing negative sanctions that can impose such a standard. Who can oversee the repairs, so that all of the participants in an interdependent system adopt a technical solution that is coherent with others in the system?
Corrupt data vs. no system: here is a major dilemma. Anyone who says that y2k is a solvable problem ought to be able to present a technically workable solution to this dilemma, as well as a politically acceptable way to persuade every organization on earth to adopt it and apply it in the time remaining, including all those that have started their repairs using conflicting standards and approaches.
Some people say that y2k is primarily a technical problem. Others say it is a primarily managerial problem. They are both wrong. It is primarily a systemic problem. To fix one component of a system is insufficient. Some agency in authority (none exists) must fix most of them. Those organizations whose computer systems are repaired must then avoid bankruptcy when those organizations whose systems are not compliant get locked out of the compliant system and go bankrupt.
If there is a solution to this dilemma, especially in banking, I do not see it.