To add to that, I have a set of Yugoslav and Zimbabwe notes that are 100% genuine, however there are printing issues (margins offset, different size, print at an angle, slightly different colors). This is quite common.
I have read that in the case of Zimbabwe they had issues finding replacement parts to keep the presses running, since they were under sanctions (same as Yugoslavia). They would not throw out the batch with small issues, also what is the point? - the money will be worthless in few days, the paper will be more worth .