there is a moral side to this... you may have hundreds of kids you dont know about, in the same area, who dont know who their siblings are, and then there is a whole hoopla... it happened in like a midwestern state. This medical student donated every week for like 10 years... had like 400 kids... they realized how mnay women had his kids when a genetic heart condition (that they didnt screen for due to the years it took place) started popping up in and around with his sons in the area...
which takes me to my next point. He had 400 kids... in the same area, around the same ages, but being raised by different families... whats the likelihood of someone banging their sister