Clinics weren't (and still aren't) supposed to pay donors for their sperm, because it's human tissue.
What they were (and are) allowed to do was reimburse sperm donors for unspecified out-of-pocket expenses, like "travel costs".
Studies have shown that up to 90 per cent of recipient parents never tell their children the truth about their origins.
Many prefer to let them think that their social parents are also their biological ones.
None of these hospitals would have had any idea where this man was donating, or how many times he had already done so.
This is because for more than 30 years there was no central register in New South Wales recording who donors were, who their children were, or even how many donor conceived babies were born.
And how many half siblings could there be, all born in Sydney, as a result of John's activity? Damien Adams is a medical research scientist, and he's also donor conceived."You could have something as little as dozens," he says.
(To most people, "dozens" of brothers and sisters is still a lot.)"But it could be hundreds, and it could be thousands, depending on the quality of sperm he had, how many straws were made, how many times it was used.
The fact that John apparently made more than 200 sperm donations to just two locations alone (Crown St Women's Hospital, now closed, and a clinic in Macquarie St) is shocking.
But on top of that he also donated at the Royal North Shore Hospital, Paddington Women's Hospital, King George V Hospital for Mothers and Babies (now closed) and at Westmead.
Her brothers and sisters are listed clinically as "Male, January, 1988", or "Female, September, 1989". Together with however many other children her sperm donor has fathered at different clinics, or with women actually in his life, the true list of Hannah's half siblings could be much longer.