If you don't understand that many rapes are unreported, then you're ignorant and you should cure that by doing some research.
If you do understand that many rapes are unreported, you shouldn't be shocked at the idea of a woman being raped more than once. And if a woman doesn't go to police, the race of the rapists doesn't come into play and is just a red herring. That's not even close to absurd-- it has absolutely happened in other cases.