Yes, Ford claimed up to 90% in the 1930s when they were producing up to 1.4M cars and trucks per year. (Down to less than 400K in the worst of the depression.)
They would go so far as to license components for in-source production from suppliers who couldn't meet the needed volume.
Still lower than farmers and their horses. :)
I suppose it makes sense, back then you wouldn't think there would be an existing supply chain of companies like Mopar just waiting for a car manufacturer to spin up and start buying their stuff