I read Mr Troyat's biography of Alexandre Dumas last year. He wrote for newspapers/magazines, often in partnership with others.Carmody wrote: First published in serialized form in L’Écho de Paris from 1891 to 1892" ... One gets the feeling he was paid by the page............
During his most successful run, he is described as pressing his partner (who produced the first draft) for work, writing his draft, and then passing the product off to the publisher in one day.
I believe Simone Bertiere's Dumas et les trois mousquetaires looks at his working method more closely - there was a court case over the credit for authorship when he fell out with his collaborator.
Mr Balzac also wrote for serial publication, but in his case apparently produced multiple drafts himself. Even on re-editions of older works. Stefan Zweig's biography of him is a good read: Balzac, le roman de sa vie.