The YEAR-TO-YYYY function converts argument-1, the two low-order digits
of a year, to a four-digit year. Argument-2, when added to the year at the
time of execution, defines the ending year of a 100-year interval, or sliding
window, into which the year of argument-1 falls.
The type of the function is integer.

Format
>>-FUNCTION YEAR-TO-YYYY--(--argument-1--+------------+--)-----><
'-argument-2-'
- argument-1
- Must be a nonnegative integer that is less that 100.
- argument-2
- Must be an integer. If argument-2 is omitted, the function will be evaluated
with a value of 50 for argument-2. At the time of execution, the sum of the
year and argument-2 will be less than 10000, and greater than 1699.
In order for the compiler to calculate the FUNCTION YEAR-TO-YYYY, the ending
year of the sliding window (or "maximum-year") needs to be calculated first.
The "maximum-year" is calculated as follows:
(FUNCTION NUMVAL(FUNCTION CURRENT-DATE(1:4)) + argument-2)
Given that the "maximum-year" above the FUNCTION YEAR-TO-YYYY is equivalent
to one of the two arithmetic expressions depending on the following condition:
maximum-year modulus 100 >= argument-1
When this condition is true, the equivalent arithmetic expression is:
(argument-1 + 100 * (truncated integer value of (maximum-year/100)))
Otherwise, the equivalent arithmetic expression is:
(argument-1 + 100 * (truncated integer value of (maximum-year/100) - 1))
The YEAR-TO-YYYY function implements a sliding window algorithm. To use
it for a fixed window, argument-2 can be specified as follows, where fixed-maximum-year
is the maximum year in the fixed 100-year intervals.
If the fixed window is 1973 through 2072, then in 2009 argument-2 will
have the value of 63, and in 2019, the value of 53.
(fixed-maximum-year - FUNCTION NUMVAL (FUNCTION CURRENT-DATE (1:4)))