When we licensed and produced Marx Trains, we visited the Marx Toy Co in Miami several times. We saw racks of tooling and drawers full of original plans and parts lists/correspondence for both toys and Trains. We noticed that there were no train tools. They were supposed to have been sold to Plastimarx of Mexico, by Quaker Oats, but the deal was never completed. A lawsuit resulted, Plastimarx sued Quaker, Quaker alleged that the tooling was worthless anyway. It became a confusing mess, out of which MDK acquired (?) a lot of the train tooling that was alleged to be missing, about the time we were starting our production. MDK got a lot of mileage out of this tooling, but is out of business now.
Bottom line, during the suit, which I testified as expert witness on behalf of Plastimarx that the tooling had real value, depositions resulted in many copies of parts lists being made. Lawyers, other expert witnesses, companies involved etc all were circulating these parts lists as exhibits. I personally had 2 bankers boxes full that I eventually trashed.
Not sure if this answered your question, but it is what I know about Marx parts lists. There could still be volumes out there.