Rational Developer for System z
PL/I for Windows, Version 8.0, Programming Guide

Subtracting dates

To subtract 2 two-digit years, y1 and y2, you need to calculate the imposing difference:

  DAYSTODATE(DAYS(y1,'YY',w), 'YYYY') -
          DAYSTODATE(DAYS(y2,'YY',w),'YYYY')
Rational Developer for System z
PL/I for Windows, Version 8.0, Programming Guide