Date::Calc has a function Moving_Window that you may find useful for converting two-digit year to four digits:

$year = Moving_Window($yy);
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That is, two-digit year numbers are first mapped to the same century as the current year. If the resulting year is smaller than the current year minus 50, then one more century is added to the result. If the resulting year is equal to or greater than the current year plus 50, then a century is subtracted from the result.