The first series from the 2021 issue, also called the interim series because it also occurs with an issue date of 2015
So the CY series was issued in 2015 and 2021.
"On the reverses of the 200 zloty banknotes of the 2015 and 2021 issues and the 500 zloty banknotes of the 2016 and 2017 issues, small rectangles embedded in the banknote's graphics contain microprints (one letter and a sequence of five digits) containing information about the printed banknote."
Cz. Miłczak "Banknotes Polskie i Wzory tom I i II", publisher NUMIS POLAND edition II 2023,
op. Cit. -Volume II, Item 212, p. 332 Curiosity?
We invite you to purchase and read the above mentioned catalog of Mr. Czeslaw Miłczak
