[fjtorres]

Originally Posted by j.p.s

I know you wrote "at least 50 years", but still...
Henry Gauthier-Villars (8 August 1859 – 12 January 1931) ran a book authoring sweatshop.

https://en.wikipedia.org/wiki/Henry_Gauthier-Villars

There's also the publishing consortia of the pulp era.
(Stratemeyer, etc)
And Alexandre Dumas is suspected of labeling as his the work of his assistant(s).
But it became a more common and regular thing in recent times.