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.
If you look at old test papers - the lack of intelligence in modern times is very stark.