You can’t trust thermostat ratings

To go along with what you, BillGrissom, are saying, I offer this corroborating story.

Many many years ago, I hung a bunch of same-rated, mixed new and used, stats in a big pot of water, by threading a tiny SS wire between the moving valve and the outter ring. Then I cranked up the heat with a thermometer also suspended in the water.
What I observed was that as the water temp increased, no two stats began opening at the same temp, nor did any two reach full open at the same temp.
I noticed that there were three different designs of stats in that pot with various sized outer "restrictor" rings, and so also various sizes of valves.
I could not find an accurate correlation between the areas of full-opening between any of them, except that some designs had larger full-open areas than others.
One of those was a hi-flow type and seemed to open faster than the others once it began opening, even tho it was late to the party. I thought that would be a good thing for my brand new alloy heads; so that is the one I installed. it was rated 195.
By IR gun thru the rad spigot and measuring thru the water, and bouncing off the cores. the water temp came up to ~205. I then hunted for a spot near the stat housing that ran the hottest, and was surprised to find two spots, one on each side of the stat house that ran a couple of degrees hotter than elsewhere. I marked those spots with black, felt-tipped marker, over the Orange-painted alloy intake. The Edelbrock heads were also painted several coats of Mopar Orange.
Over time, I measured those black marker spots, and they pretty consistently would end up at 205 to 207.
It would be impossible for me to say if the stat was fully open or not, as I cannot see into the housing. Since 2000, this stat has been working flawlessly. The box it came in was marked Milodon.
I suspect that the stat is in fact full open, as I installed a HD FORD thermostatic fan clutch,on a Seven-blade hi-attack angle fan, that limits the max water temp to 207 no matter how hard the engine is running.... or not. Between the two of them, once the engine is up to temp, it runs , by IR checking, between exactly 205 to 207.
The temperature drop in the ancient factory 26"rad, from top to bottom is 25 to 30 degrees.
Why did I choose a 195 stat for my HO 367?
Well;
partly to embarrass friends who insisted I needed a 160 stat; I'm kindof a rebel like that. and
partly because a very famous man once wrote a book and said to run my engine as hot as I could, short of a melt down. and
partly because I already knew that for max fuel-economy my engines always responded to running hotter, and this engine was built to be a daily driver, and to run on 87E10 because at that time, it was my best choice.
This engine has run 3 different cams, 3 different ratio manual transmissions, numerous different rear gears, and ended up very early in life with a GVod.
The best it has done is 32mpgUS, and the fastest track time is 93 in the Eighth (different cam).
It now has over 100,000 miles on it and has outlived the body.
That same hi-flo is still in it.