It will be quite hard to find information about the one that was there since 2021. Tanganyika didn't respond to my emails for the snow leopard information. The only source is USDA. I will just exclude Tanganyika Wildlife park from my list.
It was reported present by USDA four months ago, which is in fact more recent than the latest studbook. I would also like to point out that while your reasoning is valid, Timbavati is in exactly the same boat. There is nothing proving the horses are there except trusting the studbook. Even the regulatory agency has not recorded them present in almost four years. I consider that rather questionable and am still trying to figure out anything - it is very unusual to not be able to confirm for an animal that large.