The reason, like the problem, is simple math. Therefore, it can not be assumed that any application is Year 2000 compliant. The use of reserved values such as using 99 in the year field to indicate that a file should be treated differently in some way and introduces further complexity to the issue.
Applications affect all areas of the business.
Businesses have many automated linkages and interdependencies with correspondents and customers and rely on third party services providers or vendors for many applications. For larger businesses that deal in multiple currencies and provide wide range of products in many countries around the world, the challenge is particularly great because many of these applications are interdependent. There is no single way of fixing existing applications or databases. Different situations require different solutions. Adding two digits affects the amount of memory and storage space and, therefore, can effect performance.