Not everyone uses the Julian calendar, or even 4-digit years. Here in Japan, this is year 4 of the Reiwa era, so you need a year picker that lets you choose the correct era (Reiwa, Showa, etc.) and then the year of that era, and of course the number of permissible years per era differs greatly. (The era reflects an emperor's term, so when we get a new emperor, we start a new era.) Then, just because this system is such a PITA and anything international doesn't use it (but everything government-related does), we need a converter that lets you convert between the Japanese standard and the Julian calendar.