Invalid dates in Japanese eras?

Kip Cole kipcole9 at
Wed Sep 8 04:43:33 CDT 2021

In supplementalData.xml, the era information for the Japanese calendar has two date entries which, in the Gregorian calendar, are not valid dates.  

              <era type="186" start="1501-2-29"/>
              <era type="187" start="1504-2-30”/>

How should these dates be interpreted? I cannot find any reference in TR35. Are they intended to be interpreted as dates in the Japanese traditional lunisolar calendar?  If so, what epoch is assumed for the Japanese calendar?

Regards, —Kip

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