The Japan Mint had to hold a lottery after it was overwhelmed with demand for a proof coin set engraved with the final year of the Heisei Era.

Some 210,000 orders were placed for the set of six coins engraved with Heisei 31 during last month’s sales period, officials said Monday. The mint usually make 30,000 sets for these annual releases.

Following the deluge of orders, the mint decided to increase production to about 50,000 sets. Even so, it appears that approximately 160,000 collectors will be left empty-handed after the lottery, which took place last Thursday. Some of the sets are already being sold online by the recipients.

A name is given to the era of each reigning emperor and is widely used in calendars, media and official documents. The Heisei Era, meaning “achieving peace,” will end April 30 when Emperor Akihito abdicates in his 31st year on the throne.

Mint officials said the situation was unexpected and apologized for failing to satisfy demand. They are now worried they will again be swamped with orders for other commemorative coin sets this year dated Heisei 31.

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The coins in last week’s set, priced at ¥7,714, are minted in such a way that the motifs have a dazzling, reflective quality.