Following the "Specialized catalog of Polish coins of the 20th and 21st centuries". by Mr. Jerzy Chałupski, we encounter the following text: "August 26, 1939. The President of the Republic of Poland signed a decree published on the same day introducing steel coins of 20 and 50 groszy denominations into circulation. Steel fifty-groszy coins were to be introduced into circulation and function in parallel with nickel coins."
A coin so far erroneously attributed to the General Government, but actually minted already during the Second Republic.
Very nicely preserved.