Previous discovered files from old floppies by AW, and also ones by Keith Haring was sold as "NFT". That had the positive side effect for me to be able to extract exact copies (although not original files).
What's the difference between an original file and an exact copy?
An exact copy would be a lossless PNG (for example) of the image, that you wouldn't be able to tell the difference by looking at it when it's displayed on a screen from the original.
This person can sell the disks but I don’t think they are selling rights to the work on the disk. I think it might be similar to me selling you my DVD of Star Wars.
A classic case is a Picasso sculpture purchased by the city of Chicago in 1967. Prior to installation of the sculpture, city officials presented a model to the public. A copyright notice was put on a placard nearby, but not on the model. A lawsuit established that since there was no notice on the model, the design was in the public domain, and people could make postcards and posters of the sculpture freely, much to the city's dismay.
So yes, much of the fine art produced in the USA before 1989 is in the public domain.
I'm seeing that between 1978 and 1989 works could receive copyright protection, regardless of the display of a notice, if they were registered within 5 years.[0] Otherwise everything I'm reading jibes w/ what you're saying.
So it is possible Warhol registered these works, in which case they would be protected by copyright until 2057.
Edit: A quick search w/ LOC's "Official Public Catalog" through "Visual Material" registered to "Warhol Andy" after 1984 doesn't return any titles that look like they'd be these images. He definitely registered a ton of stuff (as would have been required for the time).
[0] https://copyright.universityofcalifornia.edu/use/public-doma....)
The copyright registration database is online [0]. He only registered a few of his art works, and these digital images are not among them.
edit: his estate registered a bunch of stuff after he died, but registration doesn't bring things back out of the public domain for pre-1977 works, or things beyond the 5-year threshold for works 1977-1989
Sound recordings were not eligible for copyright protection at all until 1972.
If the linked article is accurate and Warhol gave a disk containing the images to an engineer without a copyright notice on the disk or in the disk's contents, and without any explicit restrictions on redistribution, those images are in the public domain as well.