In the Telegraph’s story of the discovery, there’s this interesting narrative of why the canvases might have been separated and what happened to them after they were:
The Origin of the World depicts a close-up of the female anatomy and now hangs in the Musée d’Orsay. Part of Courbet’s private collection, it was considered far too risqué to exhibit at the time and could have seen the artist sent to prison on charges of “affronting public and religious morals”. […]
The explicit work was part of a much larger tableaux depicting a full female body based on Irish model Joanna Hiffernan, also Courbet’s lover. It is thought Courbet severed the head from the body to avoid any scandal for his model.
Courbet sold the most daring part of the tableau to Khalil Bey, a Turkish-Egyptian diplomat and avid collector of erotic art, who would show it to guests from behind a green curtain.
After being pillaged during the Second World War, the work was bought by the celebrated psychoanalyst Jacques Lacan and finally ended up in the Musée d’Orsay in 1995.