Would you buy a 1933 Goudey Ruth Raw?

[steve B]

As far as an outright fake goes, I believe it's possible to make one that will pass the grading companies.

There were few changes in lithography between about 1920 and the late 1980's. The sort of equipment the shop I worked for had is out of date for modern production printing but is readily available. A smallish press can be had for a couple thousand, and the other stuff is also available, camera, plate maker, cutter. Light tables are easy to make.

The stock wouldn't be that hard, I haven't looked for it, but it should be available.
Inks have changed, but the art lithography market has a lot of available inks.

Now, the question of "undetectable" really depends on who is doing the detecting and how seriously they look at things.

The angle of the cut may be different between cutters. I'll have to give it some thought, but older machines had a slightly different path for the blade. So that may be detectable.
Paper that won't react to UV is still made, almost all acid free paper doesn't include brighteners. It has a lot that's wrong, but comic book backing boards are not reactive to UV.
So with some knowledge and some looking, that gets you nearly all the way there.

Would modern stuff like inks and paper stand up to something like and XRF machine? Probably not. Unless you really really did some research to get as close as possible.

Is PSA or any other commercial TPG going to use one? No, not for the forseeable future.

I saw a fake 51 Mantle over 40 years ago. Shopped around to several dealers, very nice looking card. My local shop had it and just handed it to me and asked what I thought.
After looking at it for a few minutes "Very nice looking card, too bad it's fake"
"OK, why is it fake"
"I can't put my finger on why, but it just is."
"That's what we think, and the other 5 dealers who have seen it"

That was probably 81? While I was either still at the printers or had just left for college. Maybe 82.
I think today I could figure out the why. I'm not sure PSA could, and would bet that card eventually ended up in a very high grade slab.