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It's both - dates through April 30 are Heisei 31, and dates from May 1 are Reiwa 1, is the official take.

• earthboundkid 8y ago
  Well, I don't foresee that causing any bugs.
  • thaumasiotes 8y ago
    Bugs of that type should have been worked out long ago; it is not the norm for the era change to coincide with the new year.
    • Nullabillity 8y ago
      It is not the norm to reset your date system every 30 or so years.
      • thaumasiotes 8y ago
        ...yes it is?