Dear Alma,
There are so many interesting questions and comments, for all of which I am grateful, that I believe I missed a key question in your Mar 17@11:15 comment.
You first look for new revisions of the SG-experiment and have not had much better luck than I in finding such. It appears that from Aspect's 1982 experiment on, most, if not all experiments have been photon-based, which is another can of worms that I have not yet analyzed, as there are very significant physical differences despite the simplistic +1 and -1 logic applied. Binary counters subsume the θ-information that is quite evident in the Stern-Gerlach position-based results.
But you also mention
"Serial SG where particles are prepared in one spin position, then go through a second field and still end up in both upper and lower half planes."
You are very astute to catch this. You ask if I know whether that experiment has been performed and what is the result?
What you are describing is the scheme invented by Richard Feynman and used to develop spin-based quantum mechanics in his 1964 Lectures in Physics, vol III. It is also used to introduce quantum mechanics in JJ Sakurai's Modern Quantum Mechanics and more recently by John Townsend in A Modern Approach to Quantum Mechanics, wherein he states, on page 7 that this "modified SG device" was "introduced as a thought experiment" by Richard Feynman.
It is my belief that this is still only a "thought experiment". Moreover, Feynman often stated that the fundamental mystery of QM is captured in the "two-slit" interference experiment, and he was apparently trying to construct a spin-based analog of the two-slit interference experiment. Therefore, in my opinion, Feynman assumed that the quantum mechanical treatment of spin paralleled the two-slit quantum mechanics and proceeded to present this modified SG device as if it were true!
I have recently begun questioning this in terms of my theory, and am currently developing a simulation based on energy-exchange physics to try to model this.
I consider it entirely possible that Feynman just got carried away with his analogy and made up this physics which has been accepted as gospel for lo these 50 years. [You read it here first!] I believe it may be possible to actually perform a version of this experiment, and, although it's too early for me to be sure, I rather expect his physics to fail.
Feynman was such a genius, and so sharp-witted and sharp tongued, that I'm sure no one called him on this, as the analogy is almost perfect. But is it true? Stay tuned.
Thanks again for your exceedingly valuable questions.
Edwin Eugene Klingman