- All dates must have a four character year so that accurate comparisons and calculations can be performed. Where a two character year (e.g. DDMMYY, YYMMDD, MMYY) is supplied the century value is retrieved from the system definition data area. The year supplied is compared to a year in the data area, if the supplied year is less than or equal to the comparison year then the less than year is used. If the supplied year is greater than the comparison year then the greater than year is used.