You can find examples of overprint penetrated on the back practically on all values of this issue. Those with red overprints are pretty common, while those with black overprint are much rarer.
1945 Zagreb provisional issue, 40 kn / 1 kn, overprint on the back.
1945 Zagreb provisional issue, 40 kn / 3.50 kn, strong overprint on the back.
1945 Zagreb provisional issue, 160 kn / 0.50 kn, overprint on the back.
1945 Zagreb provisional issue, 200 kn / 12.50 kn, overprint on the back.
1945 Zagreb provisional issue, 400 kn / 0.25 kn, overprint on the back.
