Unlisted in the literature punch of the letter M (in the MW mint designation), where on the stamp it was first struck with an inverted punch of the letter W (the letter W has sides at an angle), then punched again with a punch of the letter M (the sides of the letter parallel). A variety only once listed on the market, at the 14th WDA-MiM auction a piece in a lower grading note reached a price of 3,795 PLN https://onebid.pl/pl/monety-rrr-krolestwo-polskie-10-groszy-1840-w-m-w-litera-m-wybita-na-stemplu-punca-w-nastepnie-przebita-na-m/346235. A great rarity in mint condition for specialized coin collections of the 19th century.