... the likelihood that Clive made up his entire gold coin thing.
If it is fabricated then I'm not the one who made it up.
Back in the 1990's it was actually given by a Prof to students in a London institution as an example of how the various fields etc had moved on in the proffession and why. I've been told it by two different "Proffessionals" in the field who as far as I know were not related to each other. One I knew well enough socialy that they used to joke about why I could not be part of various tests being run out of a South London teaching hospital. They were perfectly aware that I am left handed hence "The trouble with you lefties are you are not wired up right" joke. Over a meal one evening they confirmed my suspicions that "the proffession" was quite deliberately only testing "right handed people" as policy. Apparently because they knew that left handed people mucked up their results for various reasons. Which if you are not one of the ~4/5ths --or whatever it is where you are and age range you are in-- that are right handed is a tads worrying.
Next time I'm up in the Euston Rd during office hours with time on my hands I'll pop into the collection and have a chat with one of the curators assistants about looking it up in their records. They were quite helpfull a few years ago when I had some questions about the "Shrunken Head" process.
Oh the story about the Mullah and the two coins goes back to possibly medieval times. So there maybe an "apocryphal conjunction". I don't know but as the saying has it,
- Life imitates Art far more than Art imitates Life. (OW 1889)
As for searching on either Google or Wikipedia I've found not just significant historical gaps with Google significantly so for time periods prior to 1995, but also quite a few prior to 2005. Perhaps worse is that some people apparently get some value out of editing Wikipedia to point away from primary refrences. In atleast one case it was tracked down to a school teacher in East London who wanted their pupils to do "real research"... Others however are far worse which is one of the reasons a few years ago I spent quite a bit of time in the UK National Archives looking at primary sources with regards the "British Protectorates" that came about with the collapse of the Ottoman Empire.
Then of course as I've mentioned befor, there was the head of a University business school who tried to tell me I was wrong over a hacking incident in the UK...
Which by the way I had been in the middle of and personally knew all the players (Oh and had met HRH Prince Philip as well on another occasion a couple of years prior to that, but that as they say "Is a story for another day"). His mistakes were obvious he had looked it up via Google... Instead of consulting actual court records or speaking to those involved. He later stood as an MP and the electorate did themselves a favour, such that I think he lost his deposit...
But if I was you I would just do a google search on historic mental tests and coins. It turns up next to nothing... Which is odd because we know from historic records including a supreme court case (buck v. Bell) that they are used to test people. Even today waving a bright coin or similar shiny object at a six month old or more child is used as a measure of alertness an mental processing capacity, which is assessed by the childs eyes following or hand reaching out. If you try to widen the search you are likely to end up reading about punctured lungs.
Part of the problem appears to be because of the likes of Arthur Estabrook, who in the begining of the 20th Century was recognized expert in eugenics, and committed to the view that sterilisation laws was the way forward. This was then a quite common view back then both Woodrow Willson and Theodore Roosevelt were very much believers in it the former quite happy to sign such ideas into state law. With upwards of 30,000 forced sterilisations in the US and with obvious links to the same things going on in much of Europe it's a very dark chapter in twentieth century Western history which has been effectively "edited out". In essence the revised history points eugenics, sterilisation and euthanasia as a thing peculiar and distinct to Nazi Germany under Hitler, thus codified with "extream evil". When in fact it was extreamly popular in the US with side shows at county fairs and the likes, so for that matter "National Socialist" morals and ethics...
Because of that you might find it hard to get search results out of Google thus finding out about the "feeble minded" and the "alienists" that managed the "reservations" harder than it should be.
But to save you a little time try downloading,
And start reading at page 60, then ask yourself what the difference between a hot coin and a naked flame for testing?
You might then start to see why such information got "buried away" after WWII, after all it's hard to hold somebody up as extreamly evil when your own researchers and doctors were doing much the same thing...
 There once was a claim that a study of Apple's design teams showed that the population was inverted with only 1/5th being right handed. If you search hard enough you will find that Steve Jobs actually said as much in an interview with,
- And most of them are also left-handed, whatever that means. Almost all of the really great technical people in computers that I’ve known are left-handed. Isn’t that odd?
However I suspect that may not have been the case for a while as google searches predominantly bring up the likes of,
From 2010 and a half decade later,