They don't show it, they explain how to achieve it.
Stated differently, they purport to show how to achieve it, but don't show actual results. The absence of actual results ought to concern people who value evidence over unsubstantiated clains.
I have yet to see precise anechoic measurement showing true LF cutoff.
So no actual anechoic measurements of LF cutoff even exist in your view? That's a bold statement.