It's happened a few times.
One time the woman's husband died, but some sperm were saved. It was stored in a sperm bank for a year or so. Later she decided to have a baby with her deceased husband as the father. When the baby was born it was black. The lady and her deceased husband are white. She sued and during the investigation it was found that her husbands sperm had been discarded by mistake, so the sperm bank just took some from the freshest in the bank and didn't check anything else. All she got out of the mistake was $500K.