I am not sure what is going on here.
I took a course on testing way back in 1968 and one thing I remember is that IQ tests are probably the most reliable of all tests.
On the other hand, I do not believe people are getting smarter, just the opposite is more likely.
I suspect something is being rigged.
Students certainly seem dumber. I was looking at an old syllabus here from our own country, not sure how old, but it was probably 3 or 4 times the normal workload from what we have today. Heavy on Shakespeare and even requiring readings from Augustine’s Confessions to other marvelous gems.
I am quite confident that the best students in colleges today would still be but average or below average students in the universities just a hundred years ago.