Poland 2019 coins

Can anyone tell me how to distinguish whether the four 2019 coins I have are 

the 2017-2019 series (KM971,972,973,974)  
or the 2019-2023 series (KM971c, 972c, 973c, 974c)?  

I don't see anything obviously distinguishing on the coin pages, but maybe I'm overlooking something?

You might want to provide some links, also there are no KM numbers for Poland as far as I know Yeoman is used.

But the letter at the end would indicate a material change. It is often a non-magnetic to magnetic shift in cheapening the coinage maybe it's the case here too.

Apologies yes I mistakenly put KM rather than Y.

I was asking how I distinguish whether I have
N#102865

vs
N#233821

And the same for the 20 groszy (972 vs 972c), 50 groszy (973 vs 973c) and 1 zloty (974 vs 974c)

But….in light of your comment about composition I just noticed when going to back to grab those links that the composition DID change from copper-nickel to copper-nickel plated steel.

So, since mine are non-magnetic and presumably the steel plated ones would be magnetic I take it that means I have the earlier (non .c) versions.

Thank you for putting the composition line into mind!