I've heard of at least two cases where tests showed that the mother who delivered the babies wasn't the mom. In one case it looks like one of her ovaries belonged to a twin and the other was her own so two of her children tested to be a donor didn't show up as being hers.

The hard part is knowing how often this happens as there isn't a lot of testing and even then it would only be caught under very specific conditions. With men it's probably always written off as another father but with the mothers it was a little harder to explain away. In the other case they sent a court representative to take a sample at the birth of a new child to confirm that it was possible she didn't steal her older children.

But, back to ball pythons. Some of the paradox animals may be morphs combined with normal looking siblings and might breed as the normal looking het or possible het.