https://learn.microsoft.com/es-es/dotnet/api/system.globalization.eastasianlunisolarcalendar.tofourdigityear?view=netframework-4.8.1&viewFallbackFrom=net-10.0
EastAsianLunisolarCalendar.ToFourDigitYear(Int32) Method (System.Globalization) | Microsoft Learn
Converts the specified year to a four-digit year.
methodsystemglobalizationmicrosoftlearn