An error has been discovered in the gold ducats of 2021 that were minted by the Royal Dutch Mint. The pieces went first on sale in May and delivery started in September. They were mistakenly minted with the reverse of the 2020-dated piece. The reverse that was supposed to be used this year only differs slightly from the one of last year. All 895 pieces that were minted have the error. The double ducats were not affected by the error. The Royal Dutch Mint has announced that it will remint the entire mintage. People are allowed to exchange the error piece for a correct version, or also buy the correct version.
Below the 2020-dated reverse can be seen to the left. It depicts a gold bar near the bottom (south), referring to the southern trade routes. The correct reverse of 2021 can be seen to the right. It depicts a placcard to the left (west), to commemorate the charter that the Dutch West India Company received from the Seven United Netherlands for a trade monopoly in the Dutch West Indies, in 1621.
Source: Coin World (https://www.coinworld.com/news/precious-metals/2021-dutch-gold-ducat-mule-discovered)