Like most sperm banks, the repository limited the number of children a donor could father. In theory, the repository sent a donor into retirement after 10 children, making exceptions only to allow a family to have a sibling using the same donor. But in practice, repository policy may have been a bit looser, since Robert Graham did not have an easy time recruiting star donors. Several donors seem to have fathered many more than 10 children in more than 10 families. Since many of the repository's customers lived in Southern California, there is a remote but real possibility that half-siblings could meet each other (and who knows what else) without knowing it.