There is an interesting story about Croatian KM#1, 1 kuna 1941 which was supposed to be minted along with 2 kuna of the same date. Train from Germany that was carrying empty planchets to Zagreb mint was blown up in a partisan diversion and only extremely rare patterns exist in copper and zinc (together with one sided trial strikes etc). Zinc one, having the same characteristic of the coin that was supposed to be struck is considered the unique, only known example of the type. 2 kuna pieces were minted in planned quantities.
In these years artistically far superior patterns were made for many denominations in different metals, of which 10-20 is known of each, but since this circulation 1 kuna was uninteresting probably not more than a few, or even possibly that single one was ever made anyway.
Here's a photo from Viscevic catalog (who is also one of our members here)