I'm offering links to books, et cetera that you can purchase from my web site. I'd greatly appreciate it if you would purchase software industry books from my web site. You'll have to convert formats before doing simple comparisons or calculations. When storage is expanded, code should still be checked to ensure that the whole four-digits year is being processed, not just the YY part. Data structures and definitions must also be scanned, and sometimes modified, to store the extra two bytes within the code.
Windowing processes continue to work even when deriving realistically incorrect output.
With a four-digits system, invalid input data will trigger instantaneous notification. Since extra code must be added to nearly every program to handle dates, the project size does not diminish - it may even increase. Data input and output to third parties may not match their data definitions, standards, formats, or conversion timing when two-digits dates and windowing are used. Some date ranges, such as those found in scientific data, span more than one hundred years. A windowing approach would be impractical in these cases.