There's always a lag, you calibrate the test based on previous results, not future ones. If intelligence is decreasing I'd expect every IQ test to keep scoring a median lower than 100 unless taken immediately after calibration. Once it stops decreasing they'd converge again.
Even if that turns out to be true, rather than it starting to hit a ceiling where we can expect it to not consistently go in a single direction it does not alter anything I wrote, which addressed a comparison between 1956 and 2026.
The claim of a "lack of intelligence in modern times" is flat out contradicted by the data. It'd take a lot of regression to get back to 1956 levels.
People love to say this, but the whole point of IQ is that it happens to correlate well with many other, more practical measures of cognitive capability. That’s why it is used.
Other things also correlate well with many practical measures of cognitive ability, but you wouldn't be so quick to say that they're privileged the way IQ is, so there must be more to the explanation.
IQ is privileged because it's easily quantifiable by definition, testable with minimal setup and (assuming a modern test) more or less universal without cultural biases.
I mean it's certainly convenient! But that's a weak epistemic claim. Obviously, the cultural loading of g and of IQ tests is a complicated subject; I certainly wouldn't summarize it as "universal without cultural biases".